Figuring out what is a hot selling item and marketing are obviously very important factors when figuring out what to make.
However, I would suggest first figuring out what price point you want to be at. The price point will help define a market. People buy based on price.
It doesn't matter how great a piece is if it is priced wrong for what it is and the consumers you are trying to reach.
A great piece will sell itself in many ways but getting it sold in a timely manner can be difficult.
Are you looking at selling pieces at summer art fairs or your website? Are people going to come to your shop / unofficial storefront?
At least around here, various types of art fairs tend to have price limitations. I've worked art fairs for friends in the past and its odd and interesting to see how buyers make decisions. Also they have to carry it to the car, so that's something to think about.
If for your website, you'll need really good pictures to get a potential buyer excited.
A friend of mine used to make furniture to order but also always had pieces in his shop for sale. He would always complain about how much salesmanship he would have to do to sell shop pieces. People want a story for themselves and to tell their friends. What kind of wood, where did it come from, what was the inspiration, how did you do it, etc. Also don't forget to tell them about your respect for wood, love of carpentry and how this piece is so special.
Get the idea?
Hope that helps.