You're too serious, man. If performance is so important, then this is work for you, not play. I would suggest posting a picture of lolcats next to your monitor to remind yourself that this is a game.
Other than that, practice, practice, practice. Like others said, you just have to get a feel for it.
I would also suggest playing at off hour. You get to play with much higher quality of people (if not skill, then at least nicer people), and it makes the game much more enjoyable.
But yeah, rather than just practicing, also think about what you could have done to counter things that happened in a certain unfavourable game. It's a shame we don't have replays right now, otherwise reviewing and improving would be so much easier.