Prepare, prepare, prepare. Know your lines and learn as much as you can about the production. This will make sure you can answer other questions the casting agents may have.
The most important thing in any audition is to project self confidence. If you are not confident the reviewer will sense it and not have confidence in you either.
If you are auditioning, you should make sure to smile and make eye contact, and you should be careful not to get too nervous and throw up on the stage.
