1. Determine whether your work even belongs in the commercial end of things: Many artists who want commercial galleries are conflicted about what is commonly discussed (at least in many art schools) as the corrupting or irrelevant influences of the commercial art market. Personally, I have no qualms about artists who eschew the art market...in fact, I find it highly impressive if done for the right reasons. I know many artists who like to think that way about their work, though, who will just as happily sell work if it doesn't cost them anything personally. (I think of a certain neo-Marxist who attacked me at a panel discussion for being the source of all ill in the art world because I'm a commercial art dealer only to confess over vodka that he too had sold work and liked doing so.) All of which is my long-winded way of saying start off doing a bit of soul-searching. I don't agree that the commercial side of the art world is automatically corrupting. Too many amazing artists were all too happy to work within it and/or work to improve it. Still, there's no reason to assume you need a commercial gallery just because you're an artist. You may not. It should be something you choose because it fits in with your vision of your career.
Good read on getting into galleries, something I have dabbled with over the past, hell, 20 years? Well I have learned that it's not for me. But for people interested in it this is a good read. I do like that he calls it "commercial" and makes no bones about. The gallery world is the same as any other business and I think this is something a lot for struggling art students fail to understand. Art for arts sake does not exist once you contact a gallery. You are marketing a product.
Now, there are no value judgements going on here on my end, so don't get your panties in a bunch. It's just being honest. And this article will help you achieve those goals if you choose that road.