I have been using the "It's OK if you sit on my quilt" book a lot lately. It has a great section on different blocks. Some are shown as two-color, some multiple colors, and I sometimes start with a block I want to do. Then I pick the main fabric based on the way it would look in the block. What position, how large, and how many times will this fabric be shown in that particular block. Then I pull the partners. Depending on contrast value, I might go with a more solid-reading fabric, or I may go with a softer look. And with that auditioning process, I generally end up with something I like.
You know what really helped me? Participating in some of the swaps - like the Quilting Bee block of by month. In that swap, every participant declares their interest, and when you are partnered up, you make a block toward your partner's interest. It is a good way to grow creatively on a small scale.