I don't have any experience doing plays per se, but I have auditioned for things in the past and even got selected. More recently I have been performing on the piano for other people, which is awesome and nerve wracking.
- alcohol will not make the nervousness go away
- but it will ruin your audition
- practice, practice, practice! Know your parts back to front. Do the audition without the script
- be yourself. Relax! People can't see how you're feeling inside. I guess that's especially true for actors.
I hope that is some help