Go to Chamber 6 (Advanced Aerial Faith Plates) and get to the switch at the end. When you use the switch, you should get a lot of trash. Leave your portals right where they were when you got to the switch, then locate the radio that fell and retrieve it. Go back to the start of the chamber, and place a portal on the left wall at the opposite end of the chamber and one where you are going to fall when you get on the faith plate (sorry if it sounds a bit confusing it's hard to explain in text I'll link a Youtube video from Rooster Teeth down below, shoutout to him! :DD). Get on the faith plate and you should land in one of Ratman's hiding spots. Just walk around a bit and you should get the achievement!!

https://www.youtube.com/watch?v=-rtosjNiaNs

After you complete Test Chamber 7, place a portal on the wall right after the exit (there is no emancipation grill) and then place another portal somewhere where you can reach. Grab the companion cube, then go through that portal and head towards the elevator. After GLaDOS destroys the cube, the achievement should pop up.

https://www.youtube.com/watch?v=rfGU7NA2_4A

The only thing you need to do is to beat map Ricochet (Test Chamber 10) in under 70 seconds. I can only say that I recommend doing this in Challange Mode.
https://youtu.be/_ZLhi609p6g

Kinda self-explanatory, isn't it? Grab a turret with E and put it on a faith plate (Test Chamber 6 or 15).
https://youtu.be/psNMmt_R81U

During Chapter 4, GLaDOS is going to invite you to complete the last test chamber. Simply do it, and you'll get the achievement.
https://youtu.be/LBtckpQH9Kw

After you walk on the second Turret Redemption Line in chapter 5, you have to grab the "different" turret, which can be identified by its laser. You'll get the achievement immediately.
https://youtu.be/h7RQ_LySN5c

After you replace the master turret from the template scanner, simply step into the scanner.
https://youtu.be/3iQIvthi26I

There will be 3 sets of (vitrified) doors. First one's on the upper catwalk in the lake area, right after the hatch. Second one's on the catwalk opposite Pump Station Alpha; exit the lift and you should see them (watch the video if you don't get it). The third and final set is above the control room where you find potatOS.
https://www.youtube.com/watch?v=3yjz4pzcrms&t=18s

This achievement is very hard to explain in words, so I'll just link a video of doing it the easy way.
https://youtu.be/8obKLfdGwlw

Just when you get to 1970 Aperture, go to the top catwalk and follow it to the room. Jump on the furniture in the corner and get to the doors. Step outside and you'll get the achievement.
https://youtu.be/1_PF0LUfa4o

When you get past Enrichment Sphere 4 in chapter 7, you'll see a closed gate, a portalable wall and a fizzler leading to Enrichment Sphere 5. Portal to the second portalable wall behind the closed gate and enter the room (office) to unlock GLaDOS's dialogue and see the portrait.
https://youtu.be/0bHj-YAnvYI

In Wheatley's first room (the one where you only need to press a button and place two portals), don't do anything.
https://youtu.be/Nx7KJEvyojI

At the beginning of chapter 9, when Wheatley asks you to come back, come back and fall into the pit.
https://youtu.be/fnWf1JzbWF8

This one is way too hard to explain through words, so I'll just link a helpful video.
https://youtu.be/yvfULtN8E7s