I have noticed that even if you think two (or whatever number) fabrics that you don't think would look good next to each other, it somehow works when making a quilt. A large number of quilts that I have made, have been leftovers from other projects. I do the "reach in the bag and use what comes up" method, and I have to say that the quilts always look very good when they are all put together. The only thing I really try to do is to not have the same fabric in close proximity to the first one.
I just finished a(n) Arkansas Crossroads, and before that, a truly scrappy Irich Chain and they both really looked nice.