Visit: The best way to do research about the types of crafts in your area is to visit other shows in the same area. I found in my area at several summer festivals that jewelry making is a really big craft. In fact, I wondered why those crafters hadn't figured out that everyone else sells jewelry in the area. Fortunately, I don't make or even wear jewelry, so I won't overlap the six other jewelry makers in the area. Being unique can be a benefit when beginning in the craft show arena.
Ask the Organizer: The other to research this area is to ask the person who runs the craft show for a list of the crafters entered along with a description of what they do. This can give you a general idea. A good craft show organizer will be tracking what people sell and making sure that there isn't too much of the same things.
Ask Friends: Back to asking friends for their advice I've found that if you ask, most people are willing to give you their advice. One of my friends mentioned that a local lady makes tons of these type of signs:
If you haven't seen the rest of my posts in my 31 Days to a Craft Show series, be sure to check them all out here: 31 Days to a Craft Show.