Detective:
Talk to Grouse and finish his quest-line to find out who's killing Stalkers around Skvadosk.
Effect: Medical items placed into your personal box on Skvadovsk every morning.

Marked by the Zone
Survive 3 emissions by consuming anabiotics while not in cover.
Effect: If you're caught by an emission while outside, you won't automatically die. (Though you will pass out and have very little health left)

Trafficker of Information:
Sell 10 documents or PDAs to Owl, Loki, or Shulga.
Effect: Owl offers a discount on his items.

Courier of Justice:
Figure out that Flint is actually Magpie, and let Gonta / Loki / Shulga know.
Effect: Reward from whomever you tell, improve your relationship with Freedom / Duty.

A Friend of Duty / Freedom:
Give a number of key items and information (Morgan and Tachenko's PDA, information about Flint's crimes) to Duty or Freedom
Effect: A wider selection of items (of the type preferred by the faction you sided with) can be purchased from Hawaiian. However, if you've sided with Duty, he will raise his prices, while Nitro will drop his. Conversely, if you sided with Freedom, Hawaiian will give you a discount, but Nitro will charge you more for repairs and upgrades.

A Man of Balance:
Give Morgan and Tachenko's PDAs to Owl, and give the information about Flint to Gonta
Effect: Discounts from everyone (Owl, Hawaiian, Nitro), but no expanded inventory.

A Wealthy Client:
Have 100,000 (a hundred thousand) rubles in your inventory.
Effect: Traders now have a better chance to offer rare and expensive items (provided you have other achievements that align you with a faction, such as Friend of X or Boss?)

A Friend of Stalkers:
Complete a series of quests in favor of the Stalkers, rather than the bandits.
Effect: You can buy medical items at a discount from Tremor / Bonesetter. Stalkers will absolutely NOT help you fight any member of a faction they're neutral to (Duty / Freedom / Mercenaries), nor will they be any more aggressive than usual towards Mutants / Zombified / Monolith.

Diplomat:
Finish the missions Hostage and Debts peacefully, by paying the bandits.
Effect: Major reputation boost with all factions.

Mutant Hunter
Finish all of Trapper's mutant hunting quests in Yanov, as well as Gonta's Chimera hunting quest in Zaton (since that's required to unlock Trapper's final quest)
Effect: Major reputation boost across all factions. Different ammo types are placed in your personal box on Yanov on a daily basis.

Artifact Hunter:
Find one of each type of artifacts (not counting the various "altered" artifacts you'll have to find for the scientists / Beard).
Effect: High Level artifacts are more likely to spawn. You will occasionally be attacked by random bandit groups, regardless of your reputation.

Pioneer:
Bring Beard the Altered Wheel. Bring the scientists the Anomalous Plant and Altered Insulator.
Effect: Hermann has better items.

Research assistant:
Finish 4 missions for the scientists.
Effect: Discounts when purchasing items from Hermann or repairs / upgrades from Novikov.

Boss:
Side with Sultan during the Bear-Sultan quest line.
Effect: Discount and more items for sale at Owl's. 500-2000 rubles per day in tribute from Beard (as a result of completing Shady Business in Sultan's favor). No more artifact hunting missions from Beard.

One of Ours:
Side with Beard during the Bear-Sultan quest line.
Effect: Owl stocks much better items.

Leader:
Recruit Vano, Sokolov and Strider to join your team going into Pripyat.
Effect: Everyone on the team gets more health.

Seasoned Stalker:
Visit 18 anomaly concentrations, marked or unmarked on your map.
Effect: Better artifcats spawn.

Weapon Systems Expert:
Bring Cardan three tool sets (Crude, Fine, Calibration).
Effect: Cardan can now upgrade almost everything, including upgrading an exoskeleton so that you can run in it.

Hi-Tech Expert:
Bring Nitro three tool sets (Crude, Fine, Calibration).
Effect: Nitro can now upgrade almost everything, including putting an Infra-Red scanner on a Tactical Helm (allowing you to spot enemies through walls).

A Keeper of Secrets:
Save the notes from Strelok's stashes in Yanov, and give them to him in Pripyat.
Effect: Strelok will reward you with a Flame and Bubble artifact, as well as some scientific medkits. His health will increase, making it more likely that he will survive the final mission.

(Achievements you start working on while in Zaton - you'll have to travel beyond to complete most of these)

Detective:
This will probably be your first and easiest achievement. Just talk to Grouse, head towards the OakPine anomaly (get Cardan drunk on two bottles of vodka first - you'll find one of his friends a bit south of the anomaly). Afterwards, you will be called to explore the Krug Antenna Complex. You'll have to kill two Bloodsuckers (if you haven't already, before taking the quest). Once the lair is explored, wait a while, and once the quest prompts you, enter the small shack next to the Dock Cranes.

Courier of Justice:
You'll get the quest to find Magpie when you first enter the medic's room on Skvadovsk. Once you get to Yanov, Freedom member Flint will be constantly boasting that he is the one who accomplished whatever notable sidequest you've undertaken. Keep talking to him until he cracks (right away, if you got the Heart of Oasis, or after several confrontations if you've done enough sidequests), at which point you can find Splinter at the nearby Quarry. After a chat with Splinter, Flint will reveal his true colors.

Once you hand Flint over to Shulga / Loki / Gonta (depending upon which faction you want to be friends with), the quest is over - but if you turned Flint over to Freedom / Duty, you can still get a minor reward from Gonta afterwards.

A Friend of Stalkers:
This is done by maxing out your reputation with the Stalkers. You HAVE to finish The Hit and Transaction by siding with Beard (among other pro-Stalker quests, such as Debt, Hostage, and the mutant hunting quests)

Wealthy Client:
You could conceivably finish this before you ever leave Zaton, but it's unlikely. The simplest and easiest way to make money, bar none, is to fetch artifacts for Beard. After you bring him the Altered Wheel (the simplest way to deal with the ambush is to hand the artifact over, then shoot runner boy when he's about halfway to Skvadovsk) Beard will start paying you a LOT of money for rare artifacts (Shell, Firefly, Snowflake, Eye, Flame, Bubble, Goldfish, Gravi). You need better artifact detectors AND certain anomalies to get these to spawn consistently though.

Artifact Hunter:
Another quest you're highly unlikely to finish on Zaton (some of the anomalies that spawn the required artifacts are only present in Yanov / Pripyat). Here's a list[stalker.wikia.com] of all the artifacts in the game. Note that you don't need to get the Heart of Oasis or the various "Altered X" artifacts to get this achievement.

Seasoned Stalker:
Apparently, this requires exploring 18 major anomalies or anomaly concentrations. This includes unnamed concentrations, such as the Tesla anomaly in the Fine Tools train in Yanov, or the roof of the Cement Factory. I was reasonably sure that this achievement is the result of visiting most locations in the game, as I got it in Pripyat - but I might have been somewhat near an anomaly field at the time.

Marked by the Zone
Hermann starts selling anabiotics when you've finished a number of quests for the scientists, but you can find a few anabiotics in stashes before that. There are exactly three anabiotics in Zaton - two in the tunnel Grouse jumps into after exploring the bloodsucker lair (the opposite direction from the exit) and one in the "dangerous cave" inhabited by a controller, near the Burnt Farmstead (next to, but separate, from the large cavern complex).

Trafficker of Information:
The game will almost, but not quite, allow you to get this without leaving Zaton. The documents on the military convoy on the bridge next to the Ranger Station, the merc notebook and PDAs Owl asks you to retrieve and the Jupiter Plant documents should get you most of the way there. Ordering a new gun from Nimble and talking to Snag will start a quest-line that gives you two bandit PDAs, which should be enough (though there's plenty of other info out there).

Remember - keep Morgan's PDA (from "The Deal") until you get to Jupiter, and never sell Strelok's notes.

Documents you obtain in Pripyat (Monolith Stashes / Barchuk's PDA) apparently don't count for getting this achievement.

One of Us / Boss
This is probably the very first real quest you'll undertake, offered to you the moment you enter Skvadovsk. You'll be asked to help either Beard and the stalkers, or Sultan and the bandits on (what will end up being) a series of three quests. You can't get the Friend of Stalkers achievement without siding with Beard, so I'd recommend doing so.

Ambushing Knuckles' gang is easy enough (a single grenade can wipe them out) and Transaction isn't that hard either (the bandits have powerful weapons relative to your starting level, but a few grenades really clear the building). However, step 3 is fairly complicated.

First of all, you need to bring three Veles detectors to Novikov, in the scientist bunker in Yanov. You'll be rewarded with one detector while earning the Detective achievement. Another can be found inside the yellow excavator at Kopachi (loot it after going to Kopachi with Uncle Yar). Master stalkers, including zombified stalkers in exoskeletons, will occasionally have these detectors. Snag's loot might also include a Veles.

But the simplest way is just to buy them - either from Owl himself with the Wealthy Client achievement, or from Hermann, after you improve your reputation with the scientists.

After delivering the detectors, go back to Owl and let him know you've done so. Leave the Skvadovsk, and he will call you back after a while, asking you to talk to him, (then talk to Bear, then Owl again, then Sultan). You'll be asked to fetch a Compass artifact from Noah. You can:

1. Give Sultan the artifact, then get Beard another Compass from Noah when he asks you to do so. You get paid twice (20,000 rubles) and the One of Us achievement (if you sided with Beard during The Hit and Transaction, obviously).

2. Give the artifact to Beard without promising Sultan anything, or even talking to him. You only get 10,000 rubles, but the bandits are a lot less annoyed with you.

3. Give the artifact to Sultan, then chase down Beard's other artifact hunters and get their improved detectors. In order to get the artifact hunters' locations on your PDA, you need access to Beard's artifact delivery quests (having delivered the Altered Wheel to Beard). You can kill the first hunter or trade a good (non-unique) gun for his detector, then just scare the other hunter into handing the detector over. Go back to Sultan and get the achievement.

Note - Despite claims to the contrary, you need to finish all 3 quests on the same side to get this achievement.

Weapon Systems Master:
There are a LOT of guides for finding the tools, so feel free to youtube the exact locations. Here are the basics for Cardan - Tools for Basic work can be found at the Sawmill attic, surrounded by zombies. The zombies don't really start wandering around Zaton until you've explored the Sawmill / grabbed the tools, so you may want to wait a while. The Fine work tools are at Substation Workshop, guarded by a large group of mercenaries. You can try killing them all, but it's far simpler to give them 6 food items, and be granted permission to explore the area. The tools are right in the middle of where a bunch of mercs are sitting around.

There are two sets of Calibration tools in Pripyat:
One is in the Department Store basement. Follow the rodents without shooting them, and they will lead you through the maze of doors.
The other is in the Old Service Center. You'll have to get upstairs while avoiding electrical anomalies, and fight a Burer at close quarters. You can either rush the monster with your knife, or take a few shots with an under-barrel grenade launcher.

(Once again, you'll have to leave Yanov to complete some of these)

Diplomat:
After you arrive in Yanov, talk to Vano and Grizzly. Volunteer to pay the bandits in both cases. Jack, the bandit Vano owes, will try to make you pay 7000 rubles instead of 5000. If your gun is high tier enough (was expensive enough before modifications - I think pretty much every gun Nimble sells qualifies), you can threaten him into backing down.

The bandits holding Mitay hostage will settle for a high-tier artifact (like the Goldfish you're given to pay as ransom, but Firefly, Flame or Snowflake will also work). However, as you're leading Mitay out, a bandit called Dwarf will ambush you and demand a small percentage of your total $$$ as additional payment. You have to hand the money over to get the achievement.

Notes:

Completing this achievement improves your reputation with most factions, and there's no time limit, so you may want to wait until you've sided with Beard / Sultan / Freedom / Duty, before getting this, to make sure no faction turns hostile. Just consider the artifact and money to be your own in the meanwhile.

On the off chance you manage to lure Stalkers or mutants towards the bandits, they can in fact take out Dwarf without turning the bandits hostile to you, allowing you to leave without paying up. It's simpler to just spend most of your money before finishing the quest though.

Nothing to stop you from killing the bandits after you got the achievement. You won't get your money back from Jack, but you will be able to loot the artifact from Shishak.

Pioneer:
Bring the Altered Wheel to Beard, bring the Altered Insulator and Altered Plant to Ozerky.

Beard will ask you to investigate the strange glow at the Dredge Station. Go around the ship, do a bit of jumping, grab the Wheel. There are a number of things you can do once you step outside, but the simplest solution is as follows - give Tuna the artifact (the second time he asks), then run behind him, kill him when he's halfway to Skvadovsk, and grab the Wheel from his corpse.

You get the Altered Insulator during the very first scientist quest - Intermittent psy-emissions. Go into the tunnel, around the electric anomalies, into the side door, grab the Insulator, exit back into the tunnel, quickly kill the controller, profit.

To get the Anomalous Plant, all you need is some decent chemical protection (Meat Chunk, for instance)

You DON'T need to bring Heart of the Oasis to Ozersky to get this achievement.

Research Assistant:
Complete 4 of the scientist quests. You can finish Pioneer, then do a bit of anomaly studies with the research group, or on your own. If you want to make sure the research group survives, you can trade with each member and sell them some high quality guns and ammo.

Mutant Hunter:
Talk to Trapper, and complete his quests.

When hunting Bloodsuckers, you can either jump on one of the trees in the swamp or (if you're bad at detecting invisible Bloodsuckers) get a good sniper rifle and take them out from the roof of the Cement Factory.

The Burers are probably the hardest quest. They take a LOT of bullets, and you can't rush one with the knife, because other will flank and kill you. An under-barrel grenade launcher (or an RPG) can handle a Burer quickly - just make sure the grenade hits, as the targeting reticle will make you undershoot.

The Chimera hunt in Zaton is easy - circle around and shoot it directly in the head for a one-hit kill.

The Chimera at the Ventilation Complex is actually very hard. I'd combine the chimera hunt with the Heart of Oasis quest - the ladder above the Heart will take you directly to a nice sniping position the Chimera can't reach. Alternately, this might be a good place to use an RPG.

Man of Balance / Friend of Duty/Freedom:
Go through The Transaction to get Morgan's PDA. Sell it to Owl (MoB) Shulga (FoD) or Lokie (FoF). Get the scientist quest to test an improved detector, and grab Tachenko's PDA. Same deal. Finish the Courier of Justice quest, exposing Flint as Magpie, and tell Gonta / Shulga / Loki.

If you gave the information to Duty or Freedom, you can now recruit the Monolith fighters into that faction.

You can also recruit them (and get the Leader achievement) even if you're trying to get the Man of Balance balance achievement. Improve your reputation with either faction WITHOUT giving them either important PDA - the Diplomat and Mutant Hunter achievements help here. You can also get them to guard the scientists bunker (after the mercs attack you at Jupiter Plant) and give them the Jupiter documents. Finally, let the faction leader know what's up with Flint, recruit the Monolith squad, then let Gonta know you've handled matters. If you sold the PDAs to Owl, you should get MoB and (later) Leader. You don't need EVERY rep boost, but better safe than sorry.

Leader:
You can start recruiting the group once you've found and deciphered the black box AND found the documents in Jupiter Plant.
You already met Vano when completing the Diplomat achievement. Settling his debt allows you to recruit him.
Sokolov is a military pilot hanging around the scientist bunker. He can be recruited after completing the Anomalous Plant mission.
Recruiting Strider is a bit complicated. He's the head of a group of ex-Monolith cultists whose camp is near the Container Warehouse. He won't join you until his group had been adopted into a faction (Duty or Freedom).
The problem? Neither faction will take the ex-Monolith soldiers into their ranks unless your reputation with the faction is high enough. It's a lot easier to recruit the Monolith soldiers if you're also aiming for Friend of Duty / Freedom than if you're pursuing Man of Balance. See above for more details.

Hi-Tech Expert:
Plenty of video guides on how to get the tools, but a quick summary:
Tools for Basic Work can be found in a train that goes under a bridge (follow the tracks from Yanov). Climb the bridge, jump onto the train, run along the roof to the entrance, get inside. Calculate your route so that the anomaly passes you in a spot with ample room for you to sidestep it. Once the anomaly has passed, sprint to the end of the train, grab the tools, and jump out.

Tools for Fine Work are in a building at the south-west corner of Jupiter Plant. Head upstairs, avoid the anomalies (you really want to Svarog detector here), grab the tools, open the door on the upper floor, get out.

There are two sets of Calibration tools in Pripyat:
One is in the Department Store basement. Follow the rodents without shooting them, and they will lead you through the maze of doors.
The other is in the Old Service Center. You'll have to get upstairs while avoiding electrical anomalies, and fight a Burer at close quarters. You can either rush the monster with your knife, or take a few shots with an under-barrel grenade launcher.

A Keeper of Secrets:
Find all the notes Strelok's group left lying around, and keep them safe until you meet Strelok in Pripyat. Just like the tools, you can find any number of video guides, but here's a brief rundown:
1. Inside the cabin of the huge digger in the Quarry. Climb the tree to get there.
2. Under the Cement Factory. Go into the canal / river next to it, and watch the eastern shore - there's an open space filled with acid anomalies. Get past them, and find the vent with the stash in it.
3. Jupiter plant. Go south past the "main" building with the helicopter crash and documents. In the south-east corner of the plant, there's a little two-story construction. The stash is in a pipe inside the construction, among a bunch of acid anomalies.