[Keegbot]

I relieve stress by winning. Just kidding, but I like to win.

But on a more serious note...
Be rested and ready. Before a match I like to take a little time to "get in the zone" and focus. Also, it helps to have a plan for what you are going to do. If you are the driver, have your coach try and tell you what to do before teleop starts. And if you're the coach, tell the driver what to do so he/she clearly knows what to do (right at the end of auto is good). Preparation is a huge stress reliever.