Are you a hobbyist? Is there anything you like to make? I've always wanted to make and sell woodwork, so it's easy to see which way I went. I've seen a lot of people selling dolls, needlework, jams and jellies, other woodcrafts, as long as it's homemade and other people would like it you have a chance.
Get ideas from the internet, search crafts, craftshows, and on and on. Usually the "new" ideas sell great, or improvements on old ideas. A lot of people sell paper plate holders, my sister took lessons and learned how to paint, had her husband make plate holders and she would paint them up with different designs and sayings, they were a real hit.
I sold my lawn swingers real good (my own designs) and later started with the puzzles. I started with the snake and would take 8 snakes to each show and sell out! Later I started designing other puzzle animals and they sold real good. I noticed there was always something cheap for girls but next to nothing for the boys, so I started making rubber band guns, to sell at $3 and $5 each, wow! They sold real good. Later I designed my luger and shotgun for a bit more and they sold real good too.
My niece makes small pretties for girls and a few little things for boys, nothing over $5, and I've seen her outsell a lot of people. If you're unsure of what to make or sell, just make one or two of each item and try. Once you have a winner, you will have something to make over the long winters. Always store your finished items in plastic bags, don't want them to get dirty!
The "seasonal" items are quite competetive, a lot of people make different things just for Christmas, thanksgiving, etc. If you are really artistic and have some good ideas, try it!
Try out your ideas on your friends and family, realizing of course that they won't want to hurt your feelings. When you actually start selling, be sure to listen to your customers to see what they'd like. Always keep on the lookout for new ideas, ways to improve what you sell.