Contact the manager and ask to speak to them about selling your prints out of their storefront. If they say that's appropriate or what they want to do, then ask about consignment rates. Consignment is their "cut" of the sales price.
Say you sell a print for 50$ and the rate is 20%...50x0.20=10$; their business gets 10$. Pretty simple.
Usually 10-30% is what would be appropriate for a small coffee shop.
You can raise your prices as according to make up your share of the cut, but then again if you do that their cut will be higher anyway.
They want whole goods; such as a CD of your work that is ready to be sold, a print in frame, a coffee table book, etc.
That's for coffee shops.
Small galleries are a bit different; a lot of them are more formal and follow "themes." A theme is a topic the gallery is displaying images in. Smaller ones sometimes ask for people to come to them when they're running a particular theme and work with 3-6 months of planning. Some require fees, some don't. To sell out of a commercial gallery (where you would sell your work, not just display it) have consignment rates of 40-60%. This is a massive cut compared to coffee table books. Once again it's up to you to display the product and cover your own costs for the product you will be putting in their gallery.
Assuming you get into the gallery.
Gallery approaches are a bit different and more formal. Though, usually you contact the gallery director or managing director of the gallery (make sure you follow the same theme as they are showing; some can be pretty anal about that; it's no good asking a thomas kinkade gallery to show your black and white photographs...*cough*...).
Ask about representation of one of your prints in their gallery, come up with an artist's statement (telling a bit about yourself and a bit about the print) and a resume of previous experience with other galleries or businesses.
I've yet to get a call back, so take my advice on galleries with a grain of salt..though..that's how I read you're supposed to approach one..well I have had a call back I just lost their phone number oops...still working on that.
Oh one more thing; make sure for coffee shops selling your work as well as galleries (especially galleries,though) you have a contract illustrated stating your rights to the work, and most importantly your cut of the sale.
Some galleries that take you will want a cut of 50%. Okay that's 50% of your selling price out the window. If one of my prints has a selling price from me of 1200$ then add an additional 50% on top of that to make up their cut (selling price is now 2400$ sans tax). The tax is covered by their end. If they have a discount (for whatever reason) of 10% to encourage the sale of the print through their business...make sure it is illustrated in your contract that the 10% is coming from their cut and not the artist's cut.
Some smaller ones try to screw you around like that