Prepare your music until you are able to sing it without making any mistakes and from memory. One of the keys to reducing anxiety over singing is preparation. Learn the music to the point where you can sing with minimal effort. This will reduce the level of stress over your performance since you will be confident that you are able to sing the music.
Relax before going on stage. A warm-up routine of long tones and flexibility exercises will give you the proper mind-set and help relax you before you go on stage. Before going on stage, tense every muscle in your body and then relax them several times. Professionals use these techniques to help release any tension in their body.
Sing as often as possible in front of friends, strangers, at parks and in concerts. The best cure for nervousness is experience. After you have completed a few performances successfully, you will begin to feel more confident in your skill and experience less nervousness.