I get butterflies just like everyone else. So I meditate for at least ten minutes before I perform. I breathe in and out slowly for ten minutes, and that literally helps me slow my heart rate and relax.
Find the story, Granny Weatherwax always said. She believed that the world was full of story shapes. If you let them, they controlled you. But if you studied them, if you found out about them. . . you could use them, you could change them.