I'd recommend to use this guide along with one of the other guides to show you where each rabbit & poster is, as it's excellent.

"Simon Says: Don't Lose"
Complete the Simon Says game - when he asks you go to go the door & then to open the door, wait and only do so when he says "Simon Says".

"Simon Says: Good To Go"
Unmissable story achievement.

"Pull the other one"
Pull the alarm next to door (left of the teacher and man with bag on his head).

"Guitar Man"
After the tree appears, click on the guitar behind it to the left.

[Collect 4 polaroids to get the password
1) Tacked to the back of the tree
2) On the cable roll table on the right behind the tree
3) On the right wall heading towards the greenhouse opposite the milk jugs
4) On the right inside the greenhouse at the end of the train]

"Green Fingered"
Before going up to the treehouse, go to the end of the carriage into the garden.

[Treehouse password: Bluback, Wuboods, Fubor, Evuber]

"Prize Draw"
Look at the trophy inside the treehouse - to the left behind the easel

"Good Kitty"
Inside the treehouse look at the cat art to the right of the easel

"You spin me right round"
Inside the treehouse go up the ladder to the planetarium (behind the scissors). Interact with the planetarium.

"Life Giver"
Unmissable story achievement.

"Doodle Dandy"
After the room with the fire extinguisher, in the third carriage, pick up a notepad off the cabin table.

"Fire Starter"
Unmissable story achievement.

"Redemption" & "Catharsis"
These are options, if you exit out before talking to him after the achievement pops you should be able to restart at a save point just before, so that you can do the other option.
Redemption - Grab all the fires and put them back into the firepit on the balcony.
Catharsis - Grab extra fire from the fire pit and put it onto each of the burning areas.

"Who's the Daddy?"
When looking for items for the tent, inspect the bottom of the large statue down the right patch from the boat.

"Alas, Poor Isaac!"
Inspect the gravestone while looking for items for the tent.

"Pure Folly"
Go inside the folly - the small castle thing up the bank to the right of the tent, while looking for the tent items. Check the comments for someones help as this is missable!

[Pieces required to help build the fort:
1. To the side of the boat near the shore in the grass - a part of a fountain.
2. At the side of the building by the shore, on a rock - paper bunting.
3. Inside the folly at the top of the hill - a piece of vase.
4. At the base of the large statue on the ground - part of the sun-dial.]

"Big Cheater"
When you are told to count to 1000, click each of the larger number options each time.

"A Moment Captured"
After going through the tunnel, next to the Donnie Darko poster is a camera - pick it up

"Dark Destroyer"
Unmissable story achievement.

"Poster Club"
After clicking all the posters in the game at this point this achievement should pop after you get down the stairs.

"Not a happy bunny"
After collecting all the bunnies up to this point the achievement should pop here after taking the one from where the bunny was sitting.

"Masquerade"
Unmissable story achievement - triggers after the credits.