When I first started quilting 12+ years ago, I bought fabric that struck my fancy--no rhyme or reason... Now I buy fabrics that go together--mostly fall colors, but usually buy 3 to 5 colors that would go together but not blend or be monochromatic. I try to only buy when I have a pattern in mind, but I always seem to find a few fabrics that I just must have and get a few yards of each for my stash and future use...
My two favorite fabric lines are fairy frost and thimbleberries.