Obtaining Portal: Still Alive achievements

Out of the Blue
Once you have control of both portals, only enter the orange portal.

Difficulty: Very Easy
How to obtain: Once the full portal gun is obtained, the player must only enter through orange portals.

A Feeling Like Floating
Dissolve a turret.

Difficulty: Very Easy
How to obtain: Simple, just carry a turret over to the emancipation grill at the end of a level and it will dissolve.

The Camera Adds 10 Pounds
Knock a turret over with a security camera.

Difficulty: Easy
How to obtain: Use the Handheld Portal Device to detach a camera from a wall and then knock a turret over with it. Easily done in the 16th chamber by shooting a portal into the security camera that is behind the second-to-last turret in the level, close to the exit.

Like a Rat
Trap yourself in a test chamber so that GLaDOS has to help you continue.

Difficulty: Easy
How to obtain: Easiest done in Chamber 13 if you get both cubes in the first room and then shoot both of your portals onto a wall in the second one.

Tests Like Chicken
Find the chicken's test results.

Difficulty: Easy
How to obtain: This achievement requires you to find the chicken's test results which are in Escape 01 (AKA Chamber 19).

After you go past the fans, go into the office (in the back), and open the middle door. Turn to your left and pick up the Clipboard. It should say "Failed" on it and you will get the achievement.

Cupcake
Beat 5 advanced chambers.

Difficulty: Easy
How to obtain: To earn this achievement, you have to beat 5 of the Advanced Chambers, found in the main menu. It is best to go through these in order.

Saw That One Coming
Cause a rocket sentry to destroy its own rocket when the rocket has been redirected back towards it.

Difficulty: Medium
How to obtain: Make two portals directly across from each other in the room with the first rocket turret. Wait for the turret to shoot, and the rocket should dissolve, netting you this achievement.

Is Anyone There?
Complete the game without ever taking a bullet.

Difficulty: Medium
How to obtain: Sounds a lot harder than it actually is, just play smart and save frequently. If you save frequently you can re-load your last save if you get shot.

Rat's Tale
Find all the Ratman dens.

Difficulty: Medium
How to obtain: These must be done in one play through. If a room is missed, it cannot be returned to.

Chamber 16: After the first three Turrets, you should come to a pushed out wall and two cubes against the wall segments. Shoot a portal behind the wall to find the first one.
Chamber 17: After the high-energy pellet hallways, fall down and shoot a portal behind the pushed out wall.
Chamber 18: Get to the next platform in front of you and crouch into the alcove on the left.
Escape 01 (AKA Chamber 19): After you fall down the gigantic pit (You had to previously cross a giant pipe) turn to your right and go into the alcove.
Escape 01 (AKA Chamber 19): After you get past the three turrets after the previous Rat Chamber, enter the little alcove to go into an enclosed room with a turret. Do whatever with the turret, and go to the far back of this room (The wall in front of you should rise in the turret part). To your right is a little alcove with the final den.

Go for the Gold
Win a gold medal on a challenge map.

Difficulty: Medium
How to obtain: This is done by getting the best (gold medal) in either the Time Trial, Least Portals, or the Least Steps events which are on the advanced maps, however, you can only unlock the achievement by getting gold on a challenge map.

Fruitcake
Beat 10 advanced chambers.

Difficulty: Medium
How to obtain: To earn this achievement, you have to beat 10 of the Advanced Chambers, found in the main menu. It is best to go through these in order.

Vanilla Crazy Cake
Beat all advanced chambers.

Difficulty: Hard
How to obtain: To earn this achievement, you have to beat all of the Advanced Chambers, found in the main menu. It is best to go through these in order.

Video guides

Note: Not everything might be true and reliable in the videos linked here. The linked content is some form of trivia, but it can serve as a walkthrough in some way.