When you are auditioning-
Make eye contact- You want to seem confident and at ease when auditioning.
Remove jewelry, watches, or dangling things- When you're nervous you tend to play with things on yourself. I always pull my hair back and take off all jewelry.
Avoid your default position- Folding your arms, rocking back and forth, twisting, all signs of nervousness- makes the directors feel uncomfortable.
Never apologize- If you're sick, they'll know. Apologizing is like saying "I'm so sorry that you can't hear just how great I am because I happen to be dysfunctional at the moment. But I promise, every other time, I'll sound great!"
Always self-build- Never tell yourself before an audition or performance that you "are going to die!" Tell yourself things like "I can do this. I've rehearsed this. I'll make it!"
Never ask to start over- Everybody makes mistakes. What the directors will be looking for is how well you can push through them. Make it seem like you did it on purpose.
Smile, stay calm, and focus- The more at ease you are, the better.
Don't rush- It'll be over soon. Slow down, and enjoy it.
When auditioning requires you to sing a song-
Most auditions require you to sing sixteen bars of a Broadway song. If you don't know what sixteen bars is, look it up or count. Or ask someone.
Pick a song that is in your range- If you can't hit all the notes in the piece that you are singing and sound nice, this is not the song for you.
Make sure you understand the song- Understand why or how this song was originally performed. Stand in front of a mirror and speak the words. Your hands should do what you would normally do in the situation that the song gives.
Project- You might audition in a small room, but imagine that you are performing in front of a New York style audience. Be LOUD!
Bring your music- Make sure you bring the sheet music for your piece. Bringing a CD or singing acapella is not acceptable. This pianist will be able to play the song. If you need it in a certain key, tell them.
Pick your song carefully- Singing a song from a recently premiered Broadway, or movie, is not a good idea. For example if you sing Popular from Wicked, people will compare you to Kristen Chenowith. And unless you are a Broadway star, this makes you look bad. Doing a song from Les Miserables at this time after the movie just came out, might not be a good idea either.
After auditions-
If you're not called back, this doesn't mean you're not in the production, it just means they don't need to see you again.
If you don't make the part you want it doesn't mean that you are not good, it could mean that you are just not right for the part. For example (again I'm referring to Wicked) Kristen Chenowith was perfect for the part of Galinda, meanwhile Indina Mendenzel would not have been able to do as good of a job. But she worked great for Elphaba!