I often purchase "what floats my boat" so to speak. If I know that friends are having babies or if there is something special that might be coming up, I buy for that - otherwise I buy what strikes me. For me that is small prints, batiks and holiday. If there is an accompanying fabric that I like I buy that as well.
I always purchase at least 2 - 3 yds if I really like it.
Hope you have a great day out shopping!