Promotion of your music is as important as the quality of the music you perform. If you want to play for money, then you need to approach your music career as a professional. That means be well-rehearsed, own and use good quality equipment (instrument, mics, PA system, etc), and have some sort of web presence (website, ReverbNation, MySpace, Facebook, etc). Arrive early and thank the owner and employees. If the venue allows posters, make sure you produce good quality posters that are eye-catching and informative without being busy. A poster needs to give an accurate message within 5-10 seconds. An eye-catching photo (of you or your band) plus the venue name, date and time of your show. That's about it. If there is a cover charge, make sure it's on the poster. I like to put 'Tips gladly accepted' or '...graciously accepted' at the bottom as a reminder if tip collection is allowed. Don't forget to wear clothing that is clean & appropriate for the venue. Showing up in t-shirt, shorts and flip-flops may not cut it.