First of all, i want to warn you... If you completed the game once, and you got the (i dont know if its all the endings or just the true) ending, you wont be able to get achievements anymore. How to make it work again?
Delete Save01-16.rvdata2 and global.rvdata2.
Thats how you make it work.

Bully - When you go eat with Anri after she buys you chips, you can go look on the water where you get the option to push Anri into the water. If you do that and you will get the achievement called: "Bully".

Thief - Go to Anri's house with your friends and when you go into her room look into the closets, there you will get an option to steal Anri's money. If you do that, you will get the achievement called: "Thief".

Monster - At some point in the game, you can visit Felix's computer when he isn't in the lab, if you check his computer, you can destroy his project files. If you do that, you will get the achievement called: "Monster".

Linq Enthusiast - After you come on the roof at school, you will see a boy. If you talk to him, he will give you one needle with Linq in it. If you come to C (Charles) in the Infarnary you will get an option to give him the Linq, if you do that, you will get the achievement called: "Linq Enthusiast".

No Fun Allowed - At some point in the game, you will go to the TV room, Charlotte (Q84) will tell you that she is bored and you will get to choose if you want to destroy the TV screens, if you do that, you will get the achievement called: "No Fun Allowed".

Q84 Enthusiast - After Charlotte a.k.a. Q84 dies cause of her wish being granted you will get a choice to pick who you care more about, if you choose Q84 over Our Charlotte you will get the achievement called: "Q84 Enthusiast".

Ether Solutions Has a Solution For You - If you go to the TV room and watch every single TV including the microwave you will get the achievement called : "Ether Solutions Has a Solution For You".

Brainiac or Just a Cheater? - In Floor 4 you have to find a way through the gate, after you solve the riddle, you will get into a room where you have to go trough spikes, the way is shown on the sign there, if you want to get the achievement, you have to complete it without looking into the memo in your inventory. This is the sign: https://steamuserimages-a.akamaihd.net/ugc/791984865113830843/4E8B760F313D2828D8FC153DE781018F0B839A31/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

I Can Handle It, Mr. Honikker! - Keep in mind that this is extremely hard, i had to cheat doing this even tho my friend (that had to do this achievement in four people btw) helped me, so save it here and if you will have spare time after you end the game, return for the achievement, its hard, and not that worth it, trust me. If you go to floor 9 with Bennet, you will have to do a few puzzles, where you can select from your inventory to get help from Felix in the book called Honikkeripedia, if you dont use it even once in the entire floor, you will get this achievement. First part is easy, just do it alone, dont be that lazy. Second, the "classroom" is harder. You first have to add a code in to the thing thats in front of the blackboard. Figure out the code urself, its more fun! ;) Just kidding, the first code is V19, and the second that is in the back behind all the tables and chairs, is ILQG HALW. Then you can go to the "Survive" room, as i like to call it, where you have to find all the hints and then count the actual code, but dont worry, cheaters, the code is 21. Then you have to go out yourselves and create a bomb to put on the door (its easy, dont worry, I got that without any guide in like 5 minutes). And you are done! Free to go, achievement gotten right after you go from floor 9 back to Charlotte's home.

Cant say much here, i wont spoil, dont worry, if i write something too "spoilerous" i will hide it.
A Childhood's End - Aquired by choosing the Switch Channel option in the end room, as i call it. Then the Happy ending is actually going to happen.

Disposable Soul - Complete EP0.

Goodbye, Charlotte - Choose the Save Her option in the end room, as i call it. Then the two endings will happen and you will get the achievement.

Survivor - Survive tenants when they will capture Charlotte a.k.a. Q84.