Well, are you talking nerves or full-on stage fright? If you are truly afraid of being in front of spectators, then maybe live theater isn't for you.
For nerves, the best thing is to be well-rehearsed, so that not matter what happens, you can handle it. I will always be nervous presenting a new act or performing for people I do not want to disappoint. I once found out that the composer of the song I was performing to was in the audience--that was truly nerve wracking--even though I had done the act several times, it has special effect make-up that reacts differently everytime!
I always take a big breath as the em cee begins my intro and try to focus.