Ok. First off, having a certain degree of nerves is a
good thing. They give you that extra push - that adreneline - to make you really play well. But you need to
control your nerves, because if you let them take over you - you know what happens - you lose it, you play wrong notes, you forget, you panic.
You need to work on controlling your nerves. Play in front of friends and family before the "real" thing so you can work on controlling nerves. You might say you won't get nervous, but I've tried it and even just in front of my sister, I still panic sometimes.
If you are playing from memory, make sure you are 100% certain that you are confident enough and know your part enough. Then,
trust your memory. Don't doubt it. Don't think to yourself "Is that where my fingers are supposed to go?" If you think too much about it, you will lose it, your memory will slip etc. Just listen to the music and allow your fingers to do their thing. You
know it.
If you do make a little mistake, don't let it ruin the rest of the concert. Acknowledge that you made a mistake and move on. If you dwell on a slip-up, you will lose concentration and make another mistake...and another...and another, until you completely panick and throw it all away. (Can you tell I've had issues with memory and nerves??

)
My final piece of advice is this: As conceited as this may sound, go out there to
show off how good you are. This is your chance to show everyone in the audience how well you can play and how good you are at what you do. You might not be up-yourself in real life, or really believe that you are awesome, but if you go on stage feeling that way, your confidence will shine through your performance and your behaviour. You will be more confident and less nervous. You will perform better because instead of hoping that you play everything right, you know you will so you don't worry about that - you only think about the
good things, the
good bits.
Positivity. That's the key.
I hope this helped a little! If you want any more help, feel free to PM me. I'm still trying to overcome nerves - for uni I'm supposed to play by memory but so far all I've managed to do is play one piece by memory out of about three or four.
