This is a question that I don't really have a good answer for.
Most of my designs are a result of going into my studio, looking at the woods and other items I have around and playing with the materials. I read a lot of magazines and books, but most of my designs just "appear".
The more comfortable I get with something, the more I can design with it. With lights for example, I now have much more freedom to experiment because I know how to control their brightness, how to use multiple light sources in a single fixture, and, very important, what won't work. I guess my advice would be to just play with the materials until you get something you like - not much help I must admit.