Use positive self-talk before the audition to keep yourself in a productive and upbeat headspace.
Go online, and look for scripts, you can even watch a little bit on Youtube, if you find the play or musical.
Also walk in with the attitude of your character you would like to play. If you are auditioning for the villain you can walk in with a mysterious look.
When reading, hold the pages away from your face, so your words don’t get blocked out by having something in front of your face. Don’t forget to look at the person you are reading with. Get into the character you are reading. Whilst others are auditioning make sure you are reading your audition piece. Look at the people auditioning and see what people like and what they don’t like so much.
Even if you don’t get the part that you wanted, congratulate the person who got the part you wanted. It shows that you are a nice person. Don’t worry if you don’t get a main part, they’ll want to see how well you do with a smaller part first. This is especially true if this is your first performance.