This is what I learned and will help.
After playing for 4 to 5 hours, delete your temp files, and flush out your ram/memory. Then every 2 to 3 days, Defrag your computer and also flush your memory and then defrag again.
If you have windows 7 or vista, enable auto defrag. It will defrag your computer without hurting your game play.
Also one more thing. Update your video drivers.
