Here are some tips:
- Don't rehearse your piece right up until showtime. Your performance needs to be fresh. Finish your wood-shedding earlier in the day and do some scales or other exercises right before the big event.
- Perform your piece in front of your family or friends ahead of time to make yourself nervous and test your preparation. Note your mistakes and correct them for your final performance.
- During your performance, DON'T relax and enjoy your own playing! As tempting as this is, you can't afford to risk it. Keep your concentration at 100% at all times. Keep it going until the very, very last note. It's not over till it's over. You can relax during the applause, but not before.
- in general, take advantage of every opportunity to perform. The best way to cure stage fright is by getting experience in all settings. You should have a piece prepared from memory you can play on the spot for anyone who wants to hear what you sound like. I usually whip out a rendition of Harlem Nocturne.
- Now, go tear 'em up!