1. Be prepared and memorize your lines as well as you can.
2. Know who you are auditioning for. Research the casting director(s) and producer(s) so you have a sense of the style of the project.
3. Dress appropriately for the role.
4. Don't overuse props. Only use what you absolutely need to portray the character believably.
5. Don't break character. If you mess up, stay in character! Continue the audition. Wait until someone verbally cuts you to break your character.
6. Be yourself and believe in yourself. You are the only person like you. Don't try to be anyone else. YOU just might be exactly who they are looking for.
7. Have something to say when you walk into the room. If the Casting Director/Associate/Assistant asks you how you are, respond with more than "good." They want a chance to see the real you before you move into your character.
8. Be courteous in the waiting room (that applies to parents, too). Your audition starts when you pull onto the lot. You'll never know who is listening to or watching you.
9. Be professional. This IS a job interview. It just happens to be a really fun job.
10. HAVE FUN! Enjoy the auditioning process and treat it as a performance.
Top 10 tips courtesy of Bullock and Snow Casting (iCarly, Henry Danger) and Scenebot.