As per the previous Metro games, there is a morality point system which affects the outcome of the game's ending. You get morality points by doing certain things such as playing through areas of the game without killing anyone and freeing innocent prisoners.
There are also three achievements; Duke, Damir and Alyosha, which also seem to have a fair bit of weighting regarding whether you get the good ending. You can get these after completing certain areas throughout the story. You will also get an additional achievement for getting all three in one playthrough.
You will get this at the end of the mission to lower the bridge in the level VOLGA as long as Duke is alive. I personally got to the end of this mission in stealth, so didn't have a problem with Duke getting killed.
Damir stays with crew.
You will get this after fighting off Baron's assault at the top of the tower, then. I'm pretty sure for this one, you want to make sure none of the innocent slaves are killed in the previous couple areas. Guil and Damir mention it a fair bit as you enter the areas, so keep an ear out.
It sounds like there are a few additional things that will also help to determine this. For example, retrieving Guil's photo when looking for the maps and freeing villagers from a couple areas across the CASPIAN level.
Alyoshga doesn't get wounded.
Duke and Damir stay with the crew, Alyosha doesn't get wounded.
You will get these achievements by simply playing through the main story of the game.
Complete the Moscow level.
You'll get this one just after detonating the bomb on the enemy train.
Name the locomotive.
You actually get this one right near the start of the following level. During the opening cutscene of this level, the train is given a name and you'll get this achievement then.
Get into a boat.
Near the start of the next mission, where you need to go to the Church. Anna will lead you to a boat you can use to get there. Jump in and you'll get this.
Kill the Catfish.
While on your way to Krest's railcar, you'l' find yourself in a compound filled with mutant humans. Go through this area to the railcar on the other side. You'll need to drop some debris to free the track.
Lure the catfish in by dropping one of the bodies in the water, then pull the lever to free the railcar and kill the catfish in one fell swoop.
Get into the Trolley.
After dispatching the catfish, you can now enter the railcar to continue with the story.
Long distance passenger
Find the passenger train car.
Shortly after getting the rail car, you will drive it to a bandit camp. After dealing with the bandits, you can use a lever at the top of the building to open up the gate. Once it's open, you can drive the railcar through the gate and connect up the passenger car.
Lower the Bridge
Complete the Volga level.
You will get this after lowering the bridge and jumping back onto the Aurora.
Complete the YAMANTAU level.
You'll get this once you find Anna and get on out of there.
Drive the Bukhanka.
Fairly shortly after getting to the CASPIAN level, you will come across a thug who you can neutralise and take a car key. Go back to the car, and after a short cutscene you'll be able to get into the car and get this achievement.
Complete road map
Find maps in the laboratory.
Not long before the end of the CASPIAN level, Guil will guide you into the laboratory. You will eventually come across an archive with years highlighted at the edge of each shelf. After interacting with the shelf labeled 2019, a short animation will play, then you will unlock this one.
Complete the CASPIAN level.
After confronting "the baron" and defeating his forces, you will get this after a short cutscene.
Attend the wedding on the SUMMER level.
Following the CASPIAN level, there will be a wedding on the Aurora for Stepan and Katya. You will get this when you toast to their vows. Man, everything sure is great... right?
Kill 30 enemies with Tikhar.
The Tikhar is a pressurized steel ball rifle, which you will need to charge up to use.
After rescuing Katya from the church in the level VOLGA, you will return back to the train to continue the story. After talking to Colonel Miller, enter the Aurora and you'll be given a Tikhar which you can find on the left as you enter.
The kills do not need to be stealth kills, and you can kill both mutants and humans to get progress for it.
Kill a demon with fire.
For this one I found a demon hanging upside down under a bridge, which made it a very easy target.
I threw one molotov at it, and got the achievement immediately, so they're pretty weak to fire.
Kill 3 enemies using sniper scope while wearing the Gas mask and using the Night Vision goggles.
To get the Night Vision goggles, you can go past the catfish before you get the railcar in VOLGA and enter a room in the back to find the goggles at the other end of the room.
If you saved the villagers near Duke before coming here, they will reward you with a key that lets you open a door at the start of this area. This means you can get the goggle a little earlier.
Once you have them, wear them alongside your gasmask and take out three enemies with a weapon that has a sniper scope equipped. I found that the Night Vision scope I had for my Tikhar counted for this as well.
Kill 90 cannibals.
You will get this during YAMANTAU, after Anna is taken and you break free. There will be swarms of enemies at certain parts, so this will tick up pretty fast.
Make 50 kills with the Bukhanka.
During CASPIAN, you will find a car that you can drive around during this level. You can drive through enemies to kill them very easily. At night, there are more mutants around, so it could be worth driving around then.
Kill 300 mutants.
This will just tick up over time. Mutants include nosalises, watchmen, demons, etc. as well as the human mutants.
Kill 300 human enemies.
This will just tick up over time. Human enemies include bandits and cannibals.
Melee-kill or stun 50 enemies.
This only applies to contextual stealth kills where you can perform either a lethal or non-lethal takedown. If you just melee an enemy to death in-game or during a QTE, then it is not counted.
Make at least one kill with every ranged weapon.
There are ten ranged weapons that apply for this.
You shouldn't have much trouble finding each of these. Keep in mind you won't get the crossbow until the level TAIGA.
Kill 30 enemies with Crossbow.
As mentioned above, you won't get the crossbow until the level TAIGA. Once you do, just ensure you use it for a while and rack up the 30 kills.
Install a modification of each category on a single weapon.
Simples. You can find weapon modifications by getting them from weapons found in the world. Then you can place them on your weapons at a workbench or from your backpack.
Generally, it looks like standard weapons will have the following categories:
You'll need to equip one from each category to unlock this.
Friend of the Crew
Find the guitar and teddy bear on the VOLGA level.
Before you head out to find Krest's railcar, talk to Nastya and your squadmates regarding their Teddy Bear and a guitar respectively. They will each give you a location to find those items, and there will be special icons on the map for them. Go to each location and retrieve the items.
As the achievement suggests, you only need to find these items, you don't actually need to take them back to the requester. Though... you still should.
Spend 500 consumable resources on crafting.
You should get this fairly easily just in your normal playthrough. You can find resources all over the place, just check buildings and bodies of guards. Then you can spend those resources on crafting ammo, throwables, filters, medkits, etc...
Spend 500 chemical resources on cleaning weapons.
This one will take a bit longer than the above. Cleaning weapons does not require as many resources as crafting and can only be done at a fixed workbench. Go splash around in some puddles to muddy up your weapons.
Join us on air
Find a tune on the radio.
You can get this during the short levels that take place on the Aurora, like SPRING and SUMMER. Sit down at the desk in your room and interact with the radio. Cycle through the tuning fairly slowly until you come across a station just playing some music.
This is what I had it set to when I got it.
After running out of filters in a hazard zone, craft a new one while suffocating.
This one isn't too difficult if you're ready for it. If you have a big stockpile of filters, you can dismantle them at a workbench first. Then while in an area where the gas mask is required, wait for the time for you current filter to drop down to zero.
Then you can bring out your backpack and craft yourself a filter. You'll get the achievement as soon as you craft it.
Find all 70 hidden Diary pages.
Old world pictures
Find all 21 post cards.
Dressed for Success
Find all upgrades for Artyom's suit.
There are a few of each of these in most chapters. If you look in the collectibles menu, you can see which you've missed in the order they can generally be found.
As for the suit upgrades, there are 12 in total, but no way to see a list of ones you've missed in-game. I will instead list them here and include them in the following walkthrough.
I'll put a walkthrough in the following sections with each collectible's location.
Chapter #1 - Moscow
After coming across your first Nosalises of the game, you'll find a sort of alcove off to the immediate right.
This diary entry is sitting on the desk in this area.
After the first little part of the game, you will wake up in a hospital bed. When you can, move directly forwards and find Artyom's medical file on a desk on the right.
Leave the hospital room you wake up in and head into the next small room, but do not continue through the following door. Instead, look to the right and see the postcard on a locker.
Wait a week. From the start of this area, follow Anna down the first set of stairs.
Instead of continuing down the stairs, go down the corridor and enter the room with the open door on the right.
In this room you'll find the postcard next to the window on the far side of the room.
From the room mentioned above that had the postcard in it, head through the doorway on the left into the neighbouring room. You'll see a letter on a small box in this room.
Diary #4 + #5 + #10
See the video below...
After getting shot in the face dog tag, you'll soon crawl through a small opening and pick up some medical supplies.
Look straight ahead when exiting this opening and you'll find the next diary entry, near a buried skeleton.
Continue on until you reach the room with the communications jammer and you can find this entry on the console behind the angry dude.
After leaving the angry dude and making your way across the following courtyard, you'll enter a tight corridor leading to the next area.
In this corridor you'll find this diary on the workbench in the corner opposite from where you entered.
This diary is on the enemy train right near the end of the level. After boarding the other train, you'll take out an enemy as you enter the train through a window.
As soon as you get in, you can go through an opening on the right and enter the next room.
This room has a couple guards, but you should be able to grab the diary from the desk without alerting the guards.
Chapter #2 - Winter
When you can, go past Anna and head down the stairs.
At the bottom of the stairs is the diary entry on the left-hand side.
Chapter #3 - Volga
Suit Upgrade #1
After leaving the church, you'll meet up with Duke. He'll let you know about a nearby plane. Head over there and go inside. At the front of the plane you'll find the radar suit upgrade.
From the plane, start heading back towards the Aurora.
On the way, you'll come across a couple skewered shrimps.
In a small camp behind them, you can find this diary on a bedroll.
After falling down the hole and finding Anna, start going through the level.
You'll come across a grate with a padlock. Break it and enter the room.
At the end of the room on the far side you'll find the next entry.
When you're going to meet Krest at the port, look nearby for a staircase going down on the ground level.
Head down and fight off an ambush of mutant humans.
Go across from where you entered and look on a shelf directly opposite you.
Diary #4 + #5 + #7
See the video below...
On your way to get Krest's railcar, meet up with Duke at his lookout. He will drop down and let you know about a few points of interest. The one you should head for is the gas station.
After clearing out the bandits, enter the room on the left at the front.
You can find the diary on a table in this room.
Chapter #4 - Spring
When you wake up in the passenger train and leave the room Anna's in, swing a right towards where Nastya is.
Not far down the hall, look in an alcove to the right.
The diary is sitting on a table here.
Chapter #5 - Yamantau
When you get off the elevator that rotates around the outside of the silo, you'll be in front of this doorway.
Head through and look on the left side.
The diary is on a desk here.
While searching for Anna, you'll come across this room where there is a switchbox you can interact with behind a shelf on the right.
Interacting with it will light up the area behind it.
Crawl past it to get to this diary entry.
Shortly after, you will hear Miller talking about where the team should rendezvous.
In this area, stick to the right and climb over some boxes.
Afterwards, go into an office on the right side and find the diary on a low box.
Eventually you will fight a heavily armoured guy with a gatling gun.
Following that, you will enter a corridor with a few enemies.
Enter the open door on the right to find this diary.
Reunited with Anna, you will go toward an elevator.
Before entering, look to the left.
This one is sitting on a barrel just there.
Chapter #6 - Caspian
Chapter #7 - Summer
Chapter #8 - Taiga
Chapter #9 - Autumn
Chapter #10 - Dead City
Patch the Gasmask.
Sword of Damocles
Complete the TAIGA level.
Save Anna by paying the ultimate price.
Pass the putrid tunnel.
Master of the Forest
Stand your ground against the Bear at the first encounter.
Detach all train cars on the MOSCOW level.
Assume command of the Order.
Pass the Research Facility without killing a Blind One on the DEAD CITY level.
Take part in the Admiral's tea party on the TAIGA level.
Use the bucket lift on the CASPIAN level to reach the Oasis.
Destroy the biggest statue in front of the children's camp on the TAIGA level.
Not long after starting the TAIGA level, you'll come across this statue.
A single crossbow shot the head of the statue will net you this achievement.
Complete the game in Ranger Hardcore mode.
Complete the TAIGA level without attacking anyone or getting noticed.
Kill 50 enemies at long distance.