Most of us who grew up learning an instrument and therefore performing at recitals were offered various pieces of advice on how to deal with performance anxiety.
They ranged from, “Just focus and you’ll be alright!” to “Pretend the audience is wearing nothing but their underwear!” (because half-naked people are – less threatening?) to “Pretend the audience isn’t there.” That last one always baffled me: if you pretend the audience isn’t there, then why are you performing? Isn’t it for the audience? The audience you pretend isn’t there?
My teacher was different. She didn’t give advice but she made sure we were so well-prepared that any chance of “messing up” was minimal (and we practiced recovery for when mistakes did happen). We also practiced to perform, not once at a dress rehearsal but many times during the lessons leading up to a performance: how to walk up to the piano, bow, make sure the bench was at the proper height and distance, sit down, hear the beginning of the piece in our head, perform, finish, get up, bow, walk back to our seat.
If that sounds tedious – yes, maybe it was, but those are the steps involved in performing and so we practiced all of those steps until they felt natural and became part of “performing” – not just practicing your piece until it was perfect.
She also addressed the physical aspects of being nervous: feeling like you can’t breathe, etc.: she had us do jumping jacks – “faster!” – until we were out of breath and then immediately sit at the piano, and figure out what we had to do so we could perform while – initially – being out of breath. It was a good exercise, both physically, but also mentally in that the vague “nervous” became a very concrete physical sensation one could deal with.
I have since added my own ideas: butterflies in your stomach? Make them fly in formation. Shaky knees? Gently hold on to them with your hands and move them with purpose. And of course breathing techniques. All of which is meant to put you back in control, not allowing the performance and everything around it to control you.