First you rehearse. The rehearse some more. Rehearse so much that it becomes second nature. Then you put one foot in front of the other and get on stage and do what you rehearsed the exact same way you rehearsed it. Once you are done walk off the stage until you get the curtain call then walk back out there and TAKE A BOW. You did great.
Among the things that you can do to get over stage fright include gathering your confidence by practicing your lines in front of a mirror, reciting your part constantly until it becomes a part of you, have a good attitude and concentrate on what you are going to do.
i heard once that people get over stage fright by picturing the whole audience in their undergarments,,, kinda takes things off your mind and keeps you holding onto a good giggle inside. also you can practice in front of a mirror with friends or family or both watching you perform something so you can see yourself and them. it helps!.