Hey, Christie. I was never nervous when I sang at gigs. Very nervous in concert. As to plays, I had a running dream that I was on stage, alone, and had no idea what my lines were, nor what the play was.
When I was in high school, we had forensic presentations that were judged. There were only three of us in this particular drama. My "friend" never learned her little cue lines, so I had to memorize them and mine, too. Didn't work.
AWFUL! To this day, I think she did it on purpose.
I suppose that practice is the most important aspect..and of course, dress rehearsals.