Persistance, just keep sending your work to galleries that you are familiar with and that have work similar to yours. Being a good fit is important, otherwise you are wasting their time and yours.
I would not know how to do this, since I am not in one. Not true, my work is in Pierogi 2000, a well-known (in certain circles) gallery in hip Williamsburg, Brooklyn. I have a page on my website, under "shows" with the work included in the Pierogi 2000 flat files. Anyone can go and ask to see them, and they are for sale.
http://callieart.com/pierogi.html I have six works with them, the seventh was sold.
I am also showing in a gallery (the Dragonfly gallery) on Martha's Vineyard for their Flower Show. Check out the http://www.mvdragonfly.com/ They will have three of my larger works on canvas up for Mother's Day. A two week show. The gallery is in the art district, in Oak Bluffs. I got into this gallery by simply talking to the owner as I browsed, then I brow beater her with visuals of my work until she agreed that I would be a perfect addition to her annual flower show.
I was able to show at ABC Home, part of the infamous ABC Carpet family, by writing to the owner and convincing her that I was so Earth Day that if she did not hang my work for the month, well then she might as well give up her PC attitude of love and the earth. As an artist, I need a lot of love and attention.