When you first walk into the audition room, make direct eye contact with the director and maintain good posture. Introduce yourself in a clear and confident voice and have a copy of your resume and head shot ready in case the director doesn't already have it (most of the time the audition coordinator collects your resume and head shot prior to your entering the audition room). Be prepared to talk about yourself if, and only if, the director engages in conversation following your audition monologue. The director may ask you questions about your previous theatrical experience and education, and you should have articulate responses prepared.
If you are asked specifically to read a scene from the play you are auditioning for (this is often called a "side"), make sure to look up from the script periodically so the director can see your face. Do not rush, and if you are not sure how to pronounce a word make your best educated guess, but don't stop to ask the director in the middle of the scene. If you are asked to read with a scene partner, listen attentively to your partner and react accordingly to the emotion he or she gives you.
Everyone in the audition, from the coordinator to the director, wants you to do well. No one is rooting for you to fail, and everyone associated with the audition process understands what a daunting task it can be to stand up in front of a group of people and perform. If you can walk into the room with the knowledge that these people are rooting for your success, not your failure, it will help you feel supported and ready to take a risk.
Now is not the time for safe choices. Remember that the director has seen several different people read this same part, or perform this same monologue, and you need to make a bold choice in order to stand out from the crowd. However, be careful not to confuse bold with shocking. Don't wear inappropriate clothing or use other cheap tactics to stand out; let your talent and thoughtful interpretation of the text be what set you apart from the other auditions.