My guides tend to be straight forward. I will simply show you the fastest way to get 100% Achievements.
If you don't want to rob yourself of the fun you could have with this game, move along.

Also if you need help progressing in the game, leave a comment and I will help you figure it out.

Description: The nightmare begins

You will get this achievement by simply playing the game.

Description: Find the inmates list

This one is fairly hard to miss. After exiting your jail cell you will get to the security room.
Enter the room. The inmates list will be on the table to your left.

Description: Solve the "Time Trap" puzzle

After the security room you will move through another prison corridor. Pretty much at the end you will hear an alarm clock. When you enter the cell with the clock you will get trapped. Enter 8:50 on the puzzle at the wall to unlock the cell and the achievement.

Description: Find the half of the photo with Sarah on it

After the alarm clock puzzle follow the way to your right and you will find yourself in front of yet another security room. Enter it and on a barrel you will find a torn picture of a woman. Pick it up to get the achievement.

Description: Meet Ben for the first time

In the med bay you will find an old radio (in the room after the one with the beds). Turn it on and tune to
After listening to the conversation I had to walk away a few steps for the achievement to pop.

Description: Pass the first subconscious level

The codes for the first subconscious level are the following (from after coming up the stair):
1. left: Toy horse
1. right: Rhino
2. left: Truck
2. right: Plane

Description: Get discovered by the pop up creature

After the first subconscious level you will get "caught" by Roy after a while. You will wake up in a basement and you need to find matches on a barrel.
From this position in the room you have to turn around to your left and the barrel will be in the "gap".

After the "Innate Inmate" you will get into a pretty dark room with 4 levers. To open the door you need to push the levers down in the following order:
2 - 2 - 1 - 1 - 4 - 4 - 3 - 3

Description: Solve the "Sound Trap" puzzle

When you get trapped in a cell the next time (after solving the lever puzzle, when you're back to the actual prison area) you have to solve a little puzzle to get out. Arrange the little levers as following:
3 - 1 - 2 - 4

Description: Pass the second subconscious level

In the second subconscious level there are four levers. You need to set the images as following to get out:
Top
Right
Down
Left

To unlock the save in Roy's room you have to enter the combination. It's as following:
1 - 5
2 - 3
3 - 6
4 - 1
5 - 4
6 - 2

Description: Meet Ben for the final time

Unmissable. You will get this achievement by playing the game.

Description: Pass the third subconscious level + Complete the Game

After the library you will end up in the third subconscious level. When you reach the maze part just follow the yellow lights till you reach a red door which is your exit.

In the next section walk towards that yellow lamp(?) which will trigger the final achievement and a cutscene.