Practice as much as you can before the piano recital. Being completely comfortable with your music allows you to get through your recital without making too many errors, even if you are nervous.
Work through the difficult pieces you plan on playing before you learn the easier ones. This gives you more time to lock those tough passages in and nail them in the recital.
Utilize deep breathing and meditation before heading out on stage to center yourself. These are both natural ways of calming your nerves and lowering your heart rate, which allow you to concentrate and perform smoothly.
Use practice methods that help you memorize your music. Changing tempo and chunking (playing small pieces from memory) are great for sticking the music in your long-term memory.
Remember that your audience is there because they're interested in what you have to play and want to hear you perform. They're not there to judge you, contrary to how you might feel, so relax and enjoy the chance to share your music with them.
Allow the music to flow through you as you perform. Try to feel what you're playing instead of thinking about it. It's not a spelling bee, it's a piano recital, so let your expressiveness lead you through the pieces.