Well, I am a Thespian

. Realize that the few minor mistakes you make, most of the audience won't know, or won't care. Also, that energy you get before playing onstage, get rid of it. So something, jumping jacks, strum the shit out of you back stage. Or, you can find ways to calm down or meditate. Relax, read, doing ritual stuff.
Also, the biggest fear comes right when you get onstage or in front of someone. Then, wait a minute, let it soak in, and it should start to fade. Then believe in yourself, tell yourself you will do your best, and that is all you can do, and is good. Some of these are silly, but they do work, IMO.