Keep in mind that you are performing for the audience and be appreciative of it.
Your performance starts as soon as you appear on stage. Please try to avoid facial expressions that give your audience discomfort.
If you look pale because of nervousness or illness, it’s good to put on pink blush or lipstick to give a better complexion even if you are a child. In fact, when you put a bit of make-up on little kids, they get excited about it and relax more before their performance (But make sure to keep it light, just to give a better complexion).
Sometimes I see a female performer with very vivid nail colors. Although this is just a personal opinion, it is not very pleasurable for some to see, so please keep that in mind, too.
You should bow slowly and politely.
Also, I recommend deciding your standing position in advance and mark it with a piece of tape, etc. The distance from the piano and whether you can see the pianist are very important. It’s not very smart to check these points at the actual performance, so make sure to do it before it starts.
When you make mistakes during your performance, try not to show it on your face. Playing at a recital is a completely different situation from practicing at home when you are relaxed. If you don’t practice playing the music through (full rehearsal), you tend to panic at the recital when you make a mistake and it could be the cause of ruining the rest of the performance.
If you must stop playing for some reason, like strings snapped, stop playing promptly. Then, say “Excuse me.” first to the pianist and then to the audience calmly with a smile, if possible, and slowly go back to the stage wing.
When strings are fixed, go back on the stage with a smile, bow, and restart your performance. When you change the strings, make sure to talk to the pianist and decide where to pick up.
When your performance is finished, line up with your co-performers, bow slowly and go back to the stage wing.