Screensaver will likely drop frames, and possibly even crash/BSOD the system.
Screensaver = off.
"screen saver" is a misnomer anyway. If you really want to save the screen, turn if off!
No sleep, no hibernate. (Good call JP, almost forgot those.)
No internet, no programs "doing stuff" on their own, in the background.
No watching videos, playing games.
Video is mono-tasking, and it does not matter how "powerful" the computer is. ("Powerful" gets quaint every few years. Search this forum's older posts, and you'll see talk of "powerful" P4 3ghz systems with 2gb RAM! And yes, you could capture just fine on those systems.)