Yep as already suggested, competence breeds confidence. Know ur material inside out, dont be looking at the others for cues.... My first gig at 18 was in a dingey basement night club, a terrifying experience. And as we emptied the dance floor we knew we were doomed. My anxiety got the better of me and I screwed up big time cause I didnt know the tunes well enough. You'll also be shocked how weird it may sound on stage with the full band in swing. But that's where total familiarity with your material is key. Good luck.