The three most important tips for a successful performance

1. Play for people.  Play for family, friends or whomever you can get to listen.  This is very different than playing when no one is there.  It forces you to focus!  Any technically difficult parts will be more challenging when there is an audience.  You may have thought you had mastered a certain part - for most players, it shines a light on that specific part.  Be ready.
2. Record yourself.  How you perceive your performance and how your audience hears you can often be quite a reality check.
3. Visualize the performance.  Play your piece(s) through from beginning to end without your instrument.  Envision yourself effortlessly performing a difficult part.  Feel the ease in your fingers; hear the sound of these notes.  Repeated visualization will build confidence in a performer to perform certain skills under pressure.

Extra Tip:

1. The three penny system:
1. Put three pennies on your piano.
2. Play the piece.  If there are no mistakes, remove one penny.
3. Play the piece.  If there are no mistakes, remove a second penny.
4. Play the piece.  If there are no mistakes, you are done.
5. When you make a mistake, go to step 1.