When  I was young, I thought I would never overcome stage fright.  I had butterflies, shaky knees, my mind went blank and there were time I wish I visited the bathroom first.  I have learned a few things over the years that have helped me with these problems.
1. Look at where audience will sit, before you perform.  You might even sit in the front row of the audience and
   visualize the play.
2. Realize that when you make a mistake that the audience sees the puppet as making that mistake.  If there is an
   accident behind the stage, a puppet can say "Pay no attention to that man behind the curtain."
3. No one can see you behind the stage, so if a mistake is made, the audience is "forgiving" and might not know who
   made the mistake.
4. Reading from a script helps to give you confidence.  Highlight your parts, so that they can more easily be seen.
   If you forget your lines, the puppet can say "Opps, I forgot my lines, one moment please."
5. Help each other behind the stage to make sure everyone says their lines at the proper times.  (If someone has a
   free hand, they can point to the other's lines when needed.)
6. Go over your lines at least three times before you perform.
7. Lick your lips before you perform.  I don't know why this works, but a lot of actors and actresses do it.