I had a gallery show in June. It was for a really small gallery, and they approached me after seeing some stuff I put into a local-ish show for the local art association. From what I could glean from the experience, bigger galleries are kind of networked (read: good ol’ boys networks), but for smaller ones, it’s more about getting your stuff in front of them. Talk to the curators; find out what they’re looking for and how they find new artists.
All galleries have their own kind of vibe, I noticed, too. It’s kind of like writing professionally — if you pitch a fantastic article about squirrels to a magazine that only prints articles about football, you’re not going to have much luck, no matter how fantastic it is. Find the ones that your work seems to mesh with, then talk to those first.
Also, I don’t know how the local “scene” is in your neck of the woods, but out here, there seems to be an inordinate number of collectives. And by collective, I mean a gallery where you have to pay to be hung — usually a membership fee, if they accept you, and then commission if anything sells through that venue. (Plus, work hours. You often have to go be a docent for at least a certain number of hours per month, or pay another fee.) I opted NOT to go for these, personally, because the volume I’d have to sell there would be vaguely ridiculous, just to break even. (And I’m an introvert. Docent hours would turn me into a quivering mass of OH-BUT-NO.)
Ultimately, though, I think sales in general sort of depend (and vary commensurately) on the hours you’re willing to put into promoting your own work, unless you hire someone to do that stuff for you. (An agent, a marketing person, etc.)