Rule Number One: It's your audition. You can always start over. You say, "Excuse me, can I start over?" You don't need to apologize. "Actors waste so much time apologizing," say all of my casting director friends.
But overall, try resist the temptation to start over even if you think you're blowing it. Chances are, you aren't.
Every single actor in this industry has booked an audition that, by his estimation, has gone terribly. Likewise, we've all had auditions we thought we nailed that never amounted to a callback. It's your job to do the work, not judge the work. If you can stop trying to judge yourself in the room, you will stop wanting to start over. And you will audition better as well.
What's more, in an audition setting, you aren't just auditioning the material. You're auditioning yourself. So rather than starting over, save yourself! Didn't we learn more about Beyonce by the way she masked her Superbowl fall than we would have if she had done everything perfectly? If Beyonce can biff on national television, you can biff at Pearl Studios. You don't have to be perfect to be fierce.
However, here are some cases where it's totally okay to stop and start over.
1. If you can't hear your starting note.
Acoustics can vary from one room to another. Kindly say, "Could you play that again, please? I couldn't hear my note." No need to apologize. The accompanist will most likely hit your starting pitch a little harder, and you will proceed to slay. BE SURE TO THANK THE PIANIST ON YOUR WAY OUT!
2. If you have a flash of inspiration.
You've been given direction by a member of the creative team. Halfway through your read, you suddenly see exactly what he or she is asking for, and how to play it. This is the best reason EVER to stop and start over. They want you to do well! So if you can suddenly give them exactly what they're looking for, by all means, do so! Make it easy for everyone to agree to cast you.
(Tip: If I am given a piece of direction, I always take a "free spin." I say, "You mean like this?," and I read a section of the script or sing a line of the song. Then allow them to direct you further. This is an opportunity to make brave, bold, CORRECT choices, so really enjoy it!)
3. If you draw a blank.
Not on, like, one word. But on all of them. Take a deep breath and start over. Stay calm, focus. Do better, or they'll think you didn't prepare.
Here's when you should probably resist the temptation to start over.
1. If you've already asked to start over once or twice before.
2. If you're doing a scene with another actor who is also auditioning. In this case, an apology to the other actor is mandatory. He may have been giving a terrific audition, and you just threw him off his game.
3. If the piano player messes up, goes too fast or too slow, or starts playing something that's not there. (I had a piano player change my key in the middle of the song once. I stayed with it, and got called back.) Regardless of who messes up, the piano player will find and follow you. Most NYC accompanists are pretty damn fierce themselves.
At the end of the day, an audition is your chance to shine. If you think you can do better, start over. Don't apologize or beat yourself up about it. Just slay.