i think if you can return phone calls, dress neatly and professionally, show up on time - everytime, speak correct english (if applicable), and hold a fairly decent conversation your 1/2 way home. Of course the proof is in the pudding. Document your clients progress and USE THEM to get you more clients. Nothing gets new people like a good testimoinal with befor and after photos! Lastly put yourself in an ideal situation (gym or studio) or go for the in-home thing. Some systems are set up in a way that it is impossible for you to make decent money.
hope that helps