It's natural to be nervous when performing. And a couple beers really do help.
But what I do is give myself a good talking to. I say even if I miss some notes, or chord changes, even if I blow it real bad; whats the worst that can happen? The audience isnt going to take you our into the parking lot and pound you. Chances are they didn't notice your mistakes anyway. If you're playing in a bar I can garentee they didnt notice. If your band mates point out your dinks; be sure to point out theirs. There are a lot of things in life to be worried about. But take it from an old pro {60} Rock and Roll aint one of em. Rock on!!! Peace and Love

Another thing to remember is that music isn't a sport thus no competition.
Music is an art and its open to YOUR interpertation. The only thing that is truly important is how YOU feel about what YOU play. Dont be to self critical.
Like Zappa said: shut up and play your guitar.

Guitars save lives!