For photography, what sells in the smaller shows are mostly the matted prints or small framed prints if you offer them. You should have some larger pieces of framed art on the walls to attract people to your booth area. It is a good idea to have items of different price points.
In some shows, such as our local Phoenix First Fridays events, where many of the visitors are younger, art items that sell the most may be in the $20.00 to $40.00 range. On a slow sale day, it is nice to sell even a low cost item under $20.00 every once in a while to keep your spirits up. In general, you will not over the long term make a decent return unless you sell some more expensive items even if those items sell in smaller quantities.
About two years ago, I started showing and offering wrapped canvas prints as an option. While most of my works hanging on the walls are in traditional glass frames, I have about 30% on canvas. Read my article on printing photography on canvas for the fine art photographer for more information. Canvas prints make a nice presentation that the customers seem to like. It is also convenient for the customer since they are light and come ready to hang on the wall with no additional framing needed. Many full time art show photographers show the majority of their art on canvas. I let my customers know if they are interested in a larger print that I offer a wrapped canvas option. The cost of printing on canvas has dropped drastically in the last few years due to the many competitors printing canvas.
For the last few years I have seen an increase in artist selling photography on aluminum. Most sell aluminum prints around the 11 x 14 to 16 x 20 size. Some photographers offer a few in the 20 x 30 or larger sizes. On my recent trip to California, I even saw prints from paintings on aluminum. This seems to be a trend that is lasting. While printing on aluminum is still expensive, prices have come down allowing artists to have reasonable prices and still make a profit.
One advantage with aluminum prints is, the same as in canvas prints, that you do not have to frame them which brings them closer in total price to similar sized prints that are framed.
As far as which subject matter sells the best, it really varies widely. Most photographers have a variety of local landscapes taken in locations near the area or State of the art shows or exhibits that they do. Landscapes are usually visually appealing to a greater audience and perhaps easier to sell than some more artistic photography. I show Southwest landscapes since that is the area I am in and landscapes are what Interior Designers seem to want for their corporate customers.
I also try to show my unique vision of a variety of other subjects that interest me that separates my work from other local photographers. I enjoy taking photos of old rusty cars or transportation related themes as well as photographing interesting objects from the past. Each artist should find his or her own style and try to be unique. Customers can recognize the passion you put into your work and see your style which attracts them to the artwork. This customer connection to the artist leads to sales.
After a while, you will see what types of items and what price ranges that your art or craft will sell at. You should look for a pattern on which type of items you customers are most interested in and purchase. While you should only create what you are interested in, your art booth should have more space devoted to the type of items that your customers are purchasing.
Knowing which artwork of yours sells is something that only personal experience can tell you and can vary depending on the area that you show. I have also found that some of my images are very hot and sell well for a while and then just drop off dramatically. I tend to sell out of those images, replace them with newer images and then 1 to 2 years later, bring them back for a new audience that has not seem them before.