I think the advice about buying what you like is very good. I find the pieces I sell are the ones I really like the best. Partly because it shows in the creativity, and partly because when I talk to customers about them, it shows as well.
Learn as much as you can about the stones, pearls, glass beads (there are differences), all the materials that you use, people love knowledge and again it translates into the fact that you care about your product.
Know you market/regional area. I actually sell way more high end stuff because the people that shop at our market also shop in good jewelry stores. They recognize the quality and the value. I've had people buy several (4/5) high end necklaces at a time, because they know that they could only get one of them for the same price in a fine jewelry store. If I were to sell in another area I might feature all less expensive items, because that would be a better match.
Look at other vendors at the markets and fairs, not just jewelry vendors. Who is busy and why. Look at their set-up, their prices, their product etc.
Try to set up next to someone who sells something very different, but that will attract the people you want to sell to if possible. I am next to the lavender lotions and essential oils - it attracts the women, and then they move over even though they might not have come by (and vice versa, so Alice loves me too!)
If you have the ability to make connections with other vendors, do that. They will help out, and send people to you. Try to visit and talk especially to any regulars on the selling circuit. I learned a lot from the other vendors.
Good luck!
