See, getting little nervous is natural everyone does have this. No one can say that they don't have stage fright. But, if we do little home work before the final stage performing it really work wonder. No, I am not saying that you should stand in front of mirror and talk (this is something I won't suggest to anyone. It may work for some but definitely not work with me). I would suggest that before the final stage performance, one need to rehearsal things with imagination of crowd and stage.
First of all, If you need to speech on stage, you start with lite note. Like starting with some joke. Try to be comfortable with crowd and surrounding. Once you get that confident, your half work is done. If you are a singer, don't look first at crowd. Start naturally, with proper pitch. If you catch the starting perfectly, then no one can stop you.
Practice is the most important part, if you are confident in your subject, there is no need to get fear.