Practice as much as possible before your performance. You need to know your songs completely and be able to hit the notes. Gradually work up to singing in front of people. For instance, start out by singing in front of a couple friends. Then ask your friends to bring a couple people to hear you sing. Another thing you can do is go to a karaoke bar and sing a song in front of the crowd.
Work out before a performance. Exercise is a stress-reliever. It also increases the endorphins in your body, which are natural chemicals that increase your mood and well-being. Work out on a regular basis, but especially the day of a big performance. You can try things like walking, jogging or even yoga.
Practice visualization techniques. Picture yourself singing in front of a large crowd. See the smiles on the faces in the audience. Hear the applause in your mind. Focus on that feeling and practice visualization every day.
Use deep breathing techniques to relax yourself. Sit down and start breathing in through your nose. Expand your abdomen as you breathe in. Then breathe out, releasing your abdomen. You can also imagine that you are breathing in peacefulness and breathing out tension and anxiety.
Think of positive thoughts before and during your performance. Get rid of negative thoughts when they pop into your mind. For instance, if you find yourself thinking you will not hit the high note, replace that thought immediately and say to yourself you will hit the note and give a wonderful performance. Also say to yourself that the audience loves you and enjoys hearing your performance.