I am sure you have heard many stories of people throwing up, passing out or choking on stage. Don’t worry, this is a very rare occurrence. If you do happen to be one of those people who gets extremely nervous before performing, don’t eat before you sing and you should be okay. It is normal to have some butterflies before going on stage, but they go away relatively quickly. The energy you get from a case of the butterflies can be great.
If you happen to choke on stage don’t show it, just patiently wait and come back in singing when it’s comfortable and makes sense. Nine times out of ten the audience never knows. If you lose your place at an audition do the same thing. Do not stop or apologize, just keep going. I would never stop an audition piece unless the director stops you or you were never able to begin in the first place. If you do need to stop do it quickly and start again. Most people are forgiving and understand that sometimes nerves can get the best of us.
My suggestion is to go out with friends and sing karaoke. Start with a group song then when comfortable do one by yourself.