Drink lots of water - for the vocal cords, and eat a banana about 45 minutes before you're on - they have a natural beta blocker which calms you down, and makes your hands steady (if you're playing an instrument ?)

Of course if you have my luck, you might slip on the banana peel and break something, or, with all water, pee your pants right in the middle of the audition !?!

Hang in there. You can do it !