Good call on making this topic btw
I actually started making a .doc file a while ago about useful CSGO links/tutorials/whatever, but I got busy with other stuff.
Anyway, I'll be posting here whenever I come up with new stuff that could potentially be helpful to anyone.
WarOwl video about player perspective and angles, which is pretty much a must-see for every CSGO level designer out there imo: https://www.youtube.com/watch?v=5e8HZqF3cyk
AlexG (worldofleveldesign.com) about CSGO layout design:
How to design gameplay map layouts
6 principles of choke point level design
From top down layout to BSP block-in workflow
More from AlexG about CSGO on worldofleveldesign.com: http://www.worldofleveldesign.com/categories/cat_csgo.php (covering Getting started/Basics, Gameplay/Map functionality).