I figure if I like it, it goes together! I usually pick out a focus fabric, then choose colors from that to put with it. Sometime I go a couple of shades lighter or darker for the contrast, depending on the pattern. If it's a fabric I spot that just says, "take me home", I buy 3 or 5 yards. That way I have enough for whatever I need it for, plus some to go in the stash for the next project. I've always heard that if your fabric is still ugly, the pieces just aren't small enough.