I often am asked about nervousness during performance and how to cope with it. Here is what I recently responded to a young clarinetist who asked me about it:
Being nervous is part of life. I still get nervous and I have been performing for sixty-three years. Know the music as well as you can. Memorize and sing and copy it on manuscript paper, play slowly, know the intervals well by name and appreciate their characters from half step all the way to octave. Perform the music many, many times in front of anyone who will listen. Send your music out into the air of the room. Use the power of your breath to continue the stream of sound, pushing through nervousness into connection with the composer. You are there to serve the composer and send his music to inspire the listener.