When I am playing where ever I may be playing, I keep in mind most of the people listening think its probably the best damn thing they have heard in a while, seeing as most people don't play instruments. Plus, I am really confident in myself naturally, so I dont really get shaken up playing. Also, just have fun with it. Not one them fake smiles band directors and section leaders might say to put on. I have a blast when I play. If I had a camera, I would put of videos of me playing so you could see. But Ive watched recordings of me playing in various places, and I have a ball, and its visible that I am. That would probably make the best impression. It shows you love what you do. Also when you do this, it adds more of yourself into the song you are playing.