Here's a few more:
19. Hotkeys make your life easier:
CTRL + Shift + Left Click up/down = Move your center up/down
CTRL + Click = Move around the map.
While having placeables selected:
ALT + Left click dragging up/down = Adjust height
Shift + Right Click moving left/right = Spinning the selected object.
20. Be careful with the use of point light; they look good but because of shadow calculation they can become a system drain. A good thumb rule is never have a tile or object be affected by more than three lights. If you have directional light turned on, this counts as one.
21. To refer the ga_ or gc_ scripts to a PC as Target, use: $PC
22. Remember to rebake your area before testing it, each time you have changed terrain, walkmeshes or textures.