1. A good costume. That doesn't mean it has to be new or top of the line, just make sure it looks good. Not frayed or cheap looking. You can find inexpensive costumes that don't look like they cost $5.
2. Hair. Brush it, style it, curl it, add extensions, do whatever you have to do to have totally rockin' hair! Look in the mirror and make sure it looks good, front, back and sides. No bank teller hair. It's a pet peeve of mine. A belly dancer will be wearing a $1000 costume and have bank teller hair; this is not what your audience thinks of when they think of a pro belly dancer. Your bank teller hair is for,,, well working at a bank.
3. Makeup. Not too much not too little. Learn what looks best on you. What looks good on someone else does not mean it looks good on you. Go to a makeup artist and have them show you how to apply and what colors look good on you. It may take you some time to master your makeup. And yes, its another pet peeve of mine that you'll see a dancer with no makeup or way too little makeup.
4. Attitude. Have a great, positive attitude at all your gigs. Always remember you are a professional and a shining example of belly dance. As a matter of fact it is your responsibility, as you may have people in your audience that will be seeing a belly dancer for the first time.
Now this girl has got the complete look of a belly dancer down!