Furniture is going to be a tough category to crack. There's just SO many models in there already, and there are tons out there for free across the net. Your best bet is just to play the numbers game and try to add as many quality models as you can, and just keep creating and adding them if possible.
Look at some of the models in the top search results and be inspired by how their thumbnails look. Figure out a way to create your previews so that your thumbnails get clipped similarly. I have a few furniture models myself, and they used to sell ok maybe several years ago, but I don't think I've sold one in quite a while. Good luck.