Nothing beats getting out and showing your work and learning which of your creations is the most popular. It may take some time to figure this out, but once you do, you can focus on creating more like items. That's why I recommend signing up for local art fairs and festivals, and not just relying on consignment and selling online. You need to personally interact with customers and see how they react to your work and what they buy in order to discover your customer base, or demographic. Knowing your demographic, or what types of people are most interested in your work is helpful because you can focus on creating for them and marketing to them.
Since I do underwater photography and paint marine life, I thought scuba divers would be my biggest marine life photography customers. Boy was I wrong! Most scuba divers are equipped with inexpensive point and shoot digital underwater cameras these days, so they take their own pictures. I do sell some of my paintings to them because while they can all take pictures, not very many of them can paint. It's people with small children, people who love the beach and people who are decorating their bathrooms and beach houses that buy my art. Children are actually one of my biggest demographics. They are attracted to my colorful sea creature art and will bring their parents into my booth. Often, the child will fall in love with one of my pieces and the parents will buy it for them. Somethimes a child can also kill a sale. When the parent likes something and shows it to the child and they don't react, it usually means no sale. Also I love to see couples come in with infants in strollers, they will often buy my art for their child's nursery.