I always get nervous at special occasions, where you are known by the audience. Being relaxed is really important. A few weeks ago we played on a weekday evening and I had to rush after work to make the show. I was so tense that when the first fiddle tune was introduced as "Sally Ann", I played "Mississippi Sawyer". The band picked it up and everything was fine, but when I realised what I'd done I just went blank and had to stop and start over. And I've been performing since I was twelve.(and that's more years than I'm going to tell).
Any technique you can use to make you relax will help. When I'm nervous I sometimes focus on some object in the back of the room and just play or sing to it.
If you find a sure cure (other than rum) for the problem, please let us all know.
Keep singin' Mike T.