Luckily, I've never really had a problem with stage fright, 'cause I seem to be confident enough in my musical ability when I get on stage that I know I'll do pretty well. And it also helps that I've been performing in public since I was like... 5.
But when nerves do come along, there are a few things I think about to calm me down. First off, if you know the songs well enough, your body will just do it for you. If you can clear your mind enough, muscle memory will take over and you'll just do it without thinking about it. The worst I ever play on stage is when I'm thinking about what I'm doing, because when you analyze where your arms are going, where you are in the song, that mistake you just made, etc. your worried brain get in the way of your creative mind, and it screws you all up. So just chill out, let the music flow through you (as cheesy as it sounds), and you'll do great.
The second thing is that most audiences don't know anything about music. They come out for a good time, to dance, or whatever else, but almost nobody is analyzing every aspect of your performance. So even if you do mess up, nobody really notices.
Lastly, as a musician, you're an artist. A lot of people stress out about playing in front of people because they'll be judged, or when a painter shows stuff off for the first time, it's a little nerve-wrecking. But you have to think about it like this: you enjoy the music you're playing, because if you didn't, you probably wouldn't be doing it in the first place. And if YOU like it, chances are that there are a million other people out there who will like it too if you give them a chance to hear it. Think of it not so much as putting yourself on the chopping block, but rather sharing something great with the people around you. There will always be people who'll try to bring you down and say it's not good, but if you're confident in yourself and your art, I guarantee a lot more people will love it. And making people happy is always fun, right?
Good luck, and I know you'll do well.
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