Print out your script sides before auditions, if they are sent to you via email. It is important to have a hard copy that you can hold and study with.
Review the script sides as many times as you can before all auditions.
Read the script, if you can get a full copy. Most agents will have full copies, so take one with you to review and research your character.
Memorize all of your character's lines. This is especially important if you have more than 24 hours to prepare. If you truly want the role, the more you prepare the more you will impress the casting directors.
Connect with the character. Find out the past, present and possible futures of your character, and how he or she is trying to relate to the other characters in the script sides for your audition.
Research the people you will be auditioning for. The more you know about their audition styles and set up, the more comfortable you will be with the script sides during your audition. Each casting director will have a different way of conducting auditions, and a different way of using cold and warm readings from the script.