Here's a few I've picked up.
-you can right click in the 2D view's and select flip options to quickly flip selected items horizontaly and vertically
-going to Tools, options, 3D view, you can increase the model and detail render distance in hammer
-pressing
turns off those white outlines for props in the 2D view
-make sure the checkmark in the box next to AUTO in VisGroups is solid when compiling
-check that all doors function
-check that each respawn locker is unique
-check that players can change class inside their respawn room
-be sure to build cubemaps for BOTH LDR and HDR
-remember to repack the map using bsp_repack
-the
button will show a prop's collision mesh if it has one. If a prop does not have or has a weird one, pick a differant prop or use the clip, bullet block, and/or invisible texture to create one for that prop.