As others have said. Watch the video a few times. Read the comments on iFixit, and look carefully at the photos. Have another computer handy so you have a guide to look at for each stage.
Use magnetic tipped drivers, and store each set of screws in order so that reassembly is easy.
The hardest parts I found were.
1. Removing and reattaching WiFi cable. Cable is very short, and not much space to access.
2. Unscrewing logic board - very stiff/tight screws.
3. Disconnecting power cable and LED light. The former needs considerable force, and the latter is tricky and looks delicate. Read guide carefully.
4. Pushing out the logic board needs quite a bit of force on the heat sink edges. You have to push hard and then it suddenly unclips and moves. At first I thought I'd broken something...
5. RAM was ok, But a bit fiddly with the rubber bumpers. Make sure you press it down into the slot fully. Read guide.
Having said all that, it was well worth it, and I love having acres of RAM. Doubt I'll ever use all 32GB in the near future, but 8GB was too tight for me and I was having a lot of swaps caused by the iGPU and apps fighting for space. 16 GB prob sweet spot for >90% of users. But once cracking it open, it made sense to plump for 2x16.