The above responses seem pretty on the mark to me. Alot of finding your way to a gallery depends on where you are in your showing career. Sometimes that sounds like a put-down to people but I think it makes some sense that one works up through a number of different kinds of venues and exhibitions. Early on, I think anything goes. Wherever and whenever you get a chance to hang your work do it. I have a good friend- a New York based artist- whose work I first encountered in an Upstate New York Cafe. We actually met and became friends because of that show. There are also usually regional exhibitions and other juried shows that can be good ways to start getting your work seen. The next step to my mind would be regional galleries- maybe the regional arts council has a decent gallery and maybe they put out a seasonal call. I know in Upstate New York where I teach there are some very good county arts council type galleries. They're non-profit so they are less concerned with the bottom line than commercial spaces might be. These types of spaces become the step to the next point- after getting some shows under your belt so to speak- academic galleries and alternative spaces (and not just the ones that may be in your area). These spaces usually have some sort of slide review process perhaps once or twice a year. Often, you can get really great opportunities for group or solo exhibitions at such spaces. Don't be discouraged if the first round comes up cold. Keep sending out to them and remember to resend to those that you tried before- directors change, the pool of applicants changes, your work changes. All of this may ultimately lead to commercial gallery representation, but ultimately that will be a function of your location, the kind of work you make and the vagaries of the market. It's nice if it happens, but probably that wasn't why you got into making art in the first place anyway. Expect peaks and valleys and be prepared for a long haul.