First and missable achievement.
In the very beginning, starting from the bed, go to the left instead of right.
Walk as far as possible and at the end of the walk,
near a hanging box, you should get this achievement.

Missable achievement.
Before exiting the first ventilation tunnels system into the black fog at the end of one of the tunnels, make sure you visited every other tunnel. Number 25 is at the bottom of one of the tunnels. As soon as you crawl near the corpse, the achievement pops out.

Unavoidable achievement.
Pops out after crawling out from the first part of the ventilation tunnels and walking below the big mothers portrait, where the little girl was.

Unavoidable achievement.
Pops out after carefully crawling under the legs of the big spider-like creature. You should not wake him up, he'll throw some bottles around and possibly kill you.

Unavoidable achievement.
Pops out after finding out a tree with a car wreck and a tree woman creature.

Unaviodable achievement.
Pops out after watching the movie.

Missable achievement.
Pops out after finding out the number 4 square in the ventilation tunnels after watching the movie. It should be down-left-down from number 1, but again, make sure you visited every tunnel. Map drawing helps.

Missable - one of three possible ending achievement.
At the end, after leaving the ventilations, follow the girl to the end.

Missable - one of three possible ending achievement.
At the end, after leaving the ventilations, do not follow the girl.

Missable - one of three possible ending achievement.
Be extremely careful during the whole gameplay, you can only die 8 times to get this one!
And at the end, after leaving the ventilations, follow the girl to the end.

The easiest one.
You have to find out where the Credits are.
Just press the Esc key 10 times in the main menu,
both credits and achievement will pop out.