Portal

For this one you'll need to get silver medals on all of the challenges. The most efficient way to get this is to go ahead and get gold medals on all of them so that you get all three of the science achievements at the same time. I made a video guide for all of the challenge maps which you can find here.

For this one you'll need to get gold medals on all of the challenges. I made a video guide for all of the challenge maps which you can find here.

For this one you'll need to get bronze medals on all of the challenges. The most efficient way to get this is to go ahead and get gold medals on all of them so that you get all three of the science achievements at the same time. I made a video guide for all of the challenge maps which you can find here.

To get this one you have to go through the story mode and knock down all possible cameras in one go (33). If you get to the end of the game it will reset your counter so be sure to do all of them in one play through. I made a video guide for this. The link to it is here.

To get this one you'll need to find all 26 of the hidden radios and take them to catch a signal for a Morse code. A link to a video guide I made for this is here.

You can get this achievement on Chamber 15 and a few others, but this is the one that I did it on. You just need to put a portal on the ceiling above you and one on the floor directly beneath it so that you infinitely fall through. Eventually the achievement will pop up. The link to the portion of the video where this is covered is here.

For this one you can get it done close to the very end of the game in the giant room with a muddy trench at the bottom. Once you get all the way up to the top you can put a portal on the slanted platform directly below you, and one on the top one across from you. If you line it up correctly you'll fly through a few times and get the achievement to pop up. The link to the portion of the video where this is covered is here.

For this one you'll need to complete 6 of the advanced maps. For a video guide of all of the advanced maps go here.

For this one you'll need to complete 4 of the advanced maps. For a video guide of all of the advanced maps go here.

For this one you'll need to complete 2 of the advanced maps. For a video guide of all of the advanced maps go here.

For this achievement you'll need to grab a turret and use it to physically knock another turret over. You can do this on Chamber 16 with any of the turrets on the level. (And there are a lot.) The link to the portion of the video where this is covered is here.

You'll get this achievement at the very end of the game after you have defeated GlaDos. The link to the portion of the video where this is covered is here.

This achievement you'll get at the end of Chamber 19. Once you get to the giant fire pit and portal over to safety the achievement will pop up. The link to the portion of the video where this is covered is here.

You'll get this achievement on Chamber 11 of the story once you pick up the orange portion of the Portal gun. The link to the portion of the video where this is covered is here.

This achievement you'll get at the very end of Chamber 17. Once you throw your companion cube bud into the incinerator the achievement will pop up.
I made a video guide for this also. The link to the portion for this is here.