1. Record and check yourself during practice.
While you are playing, you are probably listening to your own music at around 60% of your full concentration, even if you think you are fully paying attention. When the day of your actual performance comes, your hearing ability lowers even more, so the rate will be down to around 40% at most.
So, you should record yourself during practice and strengthen the good points and improve the weak points by listening to your own performance. This allows you to be objective, which is a very crucial element. This is very similar to checking yourself in the mirror before you leave to school or work, or even going up on a stage. Even when you know you are appropriately dressed and your hair is combed, you would probably still check yourself in the mirror.
So, in order to listen to your performance objectively, I strongly recommend recording yourself when playing the entire piece etc. This is very effective for making improvement. I, of course, practice using recording devices too.
2. Mental Practice.
Unexpected things happen on stage, all the time actually. For instance, you are bound to experience discomforts such as the room being too hot / cold / loud, audience being too close, or the sound system being awful. The biggest problem in such situations is focusing on the surroundings so much that you can’t concentrate on your own performance. If you blame the surroundings, I’d have to say you haven’t matured as a performer yet, because a real performer doesn’t stop for anything until his or her performance is finished.
The important thing is not to expect a perfect environment for you to play in. It’s better to expect the worst environment possible, if you want your performance to be at its best at the recital. Practice being prepared for the worst. You need to cultivate the ability to concentrate and mental strength to complete your performance in any type of situation you may be in. Full rehearsals play an important role here, too.