It’s a pretty large field to cover in a post. It would depend on whether it’s close-up, stage or walk around, or street magic. In general, however, I think its important to have the audience, no matter how big or small, on your side. They should begin by liking you. How do you get them to do that if they don’t know you? It’s that first impression that going to help or hinder you. How do you start your show? How do you dress? Are you well groomed? What are the first words you utter? How do you introduce yourself? Are the effects you perform appropriate for the particular crowd you are performing for? How do you react if you screw up a trick? How do you treat your volunteers? Everything counts. How do you engage the people? You could have a great show but have you connected personally with the audience?
These are things you should think about before you get on stage. A lot of this comes with experience, of course. Something works, you leave it in, it doesn’t, you take it out.