I seem to be at my best when I play a lot of games, so I'll play games for a few hours. So lets say I'm playing an RTS (strategy) game, I'll play a match, which ranges between 20 and 40 minutes, and once that finishes I'll do some work. The work is usually a question or two, or reading a paragraph or two. Then I go back to another game.
I like to think of it as mental conditioning.
I also make sure I regularly go to the gym, just so my body doesn't build up any stress.