Performance anxiety is something that all musicians suffer from, however some find it easier to deal with than others. It is very easy to let nerves affect your performance, but there are some ways to deal with them.
1. Perform as much as possible
If you suffer from performance anxiety it is very easy to let yourself avoid performing as much as possible, however if you never perform you will never truly learn how best to deal with your nerves. Take as many opportunities to perform as possible, it will get easier.
Breathing is one of the most important things you can do to calm yourself. Before you go on take some deep breaths slowly in through your nose and out through your mouth. This will truly help you to relax. Don't forget to breathe during the performance too. Breathing is one of the first things to go when we are nervous. Write "breathe" on your music, in important places and if you have a rest in the middle, take some more deep breaths (don't forget to count though!).
3. Believe in Yourself
Tell yourself "I can do this", reassurance is very important. Standing up in front of an audience is a very hard thing to do, be proud of yourself for having the courage to do it.
4. Rescue Remedy