PRACTICE
Stage presents begins first and foremost with practice. Know your music and the accompaniment inside and out.
How much should you practice? Consider how an athlete prepares for a competition. Just think about the time it takes to do something over and over until you can do it under pressure and do your best. Make that your goal.
It is very helpful if you can have even one rehearsal in the performance location. You will sound different in different rooms and a room bigger or smaller than your practice room may have a surprising effect on your musical result. Have friends or family be your audience for a more authentic experience.
APPEARANCE
You must dress in a way that tells your audience that you are serious about what you are about to present. All black, black and white, tux, gown, all are acceptable. Dress up but feel comfortable. Feel handsome or beautiful. Practice with your concert clothes on once to sort out any issues. Check yourself out in a 360 degree mirror.
Note: A sweating forehead which runs into your eyes can be resolved with antiperspirant applied to your forehead.
To keep adrenalin under control, be sure you eat something shortly before you perform. You may have to experiment to see what food works for you. Some people like a banana and some a protein bar for example. It usually does not work to eat a big meal close to performance time. Have a snack back stage with you. Many say a banana ½ hour before hand really helps with nerves.
ARRIVAL
Arrive at the venue early. That means you need to know how to get there, where to park, whether you need money to park, what door to go in, who has the keys to get in etc. Find a place to warm up. Check that the stage is set the way you want it. Arrange the piano and your music stand appropriately. Did you bring flowers for the stage? How about programs? Who is passing them out? This also means communicating with your accompanist or fellow performers and the venue coordinator on ALL details. Make yourself a checklist for performances to make sure that anything forgotten is only forgotten once.
PRESENTATION
This is not focused on you. It is focused on the music. Stop trying to be nervous about what people will think of you. Only focus on the music you are creating. They did not come to see your or talk to you, they came to hear you perform. Not because you will be perfect, but because they are interested in what you are doing and are there to support you. The music is center stage.
BOW
Be sure to bow. Accept the applause. Speak to everyone as if you did the best job ever. Accept all compliments. Never tell someone from your audience that you missed a spot or did not do as well as you would have liked. There will be time later for you to review your performance. Now is the time to enjoy where you are in learning to make music.