Two of the most important things to learn are how to start and when to quit. Do not force yourself on anyone at any time as that is being a boor. Do one or two things for people and then STOP.
Understand that there is a huge difference between politeness and interest. What you assume is interest and fascination may be nothing more than common courtesy. Learn to spot the difference.
Make what you do important. Don't be in a hurry to perform and don't perform in a needy manner.
Read Emily Post or Miss Manners about proper etiquette and good manners. Read Dale Carnegies How to Win Friends and Influence People as it will give you invaluable advice.
Dress at least as well, if not better than the people youre working for.
Do not overstuff your pockets so you look like youre going on a camping trip.
Have a solid, entertaining repertoire of material that you can do a 20 minute set but make it modular so you can stop at any point.
Learn the mechanics so thoroughly that you can do your effects in your sleep and not have to think about them when you are performing. That is the level at which you should begin performing for the public, not before as you will be able to concentrate on entertaining your audience.
Be serious about your work and not yourself because what youre doing is providing a bit of diversion, taking people out of their day-to-day lives for a few minutes, not showing them the cure for cancer.
Respect your audience, smile at them and remember that you are providing an entertainment service. Youre not there to show them how clever you are.