I'm a very shy and not so confident person, but the wierd thing is I dont suffer from "stage freight", I get a little nervous, but when I'm on it's ok....
Right, just think of the worst thing that will happen, and remember it will NEVER come to that...
If your playing complicated stuff, make sure you've rehersed it so much you could play it in the dark, cos when your hands shake you'll feel like you've just started playing guitar again....
Try your very best not to think about it on the days leading upto it, as I used to have this problem with my exams (not music related), when you keep thinking about it and about how difficult it is you'll panic on the day...
Be optimistic...
Have fun for GOD's SAKE!!
GOOK LUCK!!
ps if your singing make sure you've had plenty of water and quickly go over some of your stuff before you go on, cos you'll find your voice getting higher and higher the more nervous you get, but getting adjusted is easy..
A teaspoon full of leamon jiuce is suppoused to help, but I've never use so I dont know..