First, you must do ALL the work. The key to not getting nervous is to BE PREPARED!
I record myself every day with a video camera. As soon as I turn the camera on, I get an adrenaline response, exactly what I feel on stage.
I try to trigger my stage fright every day. After the thousandth time, I'm simply not bothered by nerves.
stop at a mistake during a practice performance, even if that means playing nonsense for a few bars. Also, make sure you engage your mind, by that I mean, see the music in your mind's eye. Lastly, audiate as clearly as possible. In your mind, you must first hear EXACTLY what you want to play, then make sure you play EXACTLY what you hear in your head. This is not an easy task, but if done correctly, you will have the most secure performance possible.
Also, immediately before a recital, try to convince yourself that you don't care about messing up. The stage is NOT the place to worry about something you couldn't possibly fix. If your pieces have flaws, realize that you probably will have a few slips. That's O.K.!
If you need proof of this, listen to this recording of Vladimir Horowitz. Not two seconds into the first piece he screws up royally. In spite of his errors he gives a phenomenal performance.
http://star.walagata.com/w/lapeter/horo ... oncert.wma
Ask yourself. "Which is better, note-perfection with the artistic vision of an assembly line or, an artistic performance despite flaws?" I think you know the answer to that one.
My point is, even the greatest of the great make mistakes. Chopin himself made plenty, as did Mozart, Beethoven and Rachmaninoff. What made them different is that they didn't do note-wise playing. If a piece is played correctly, there is a continuity that makes wrong notes inconsequential.