Stage fright

Does anybody have any like super amazing, guru tipes to help. I have horrible stage fright, I start to play and my arms, and mouth like vibrate, it messes up my tone, mouth, vibrato, and I'm just sick of it. I have a huge competetion this week and I want to do well. I've heard taking magnesium supplements will relax your muscles, but I'd like to get more advice.
Thank you and hope everyone had a good holiday!