I've been quilting for over 40 years and have the stash to prove it! About 10 years ago I started making only smaller projects and was happy to discover that by only buying half or quarter yards I can increase the variety in my stash. I've gotten to know which styles of fabric I'll use more of so I'll buy more of them.
I've learned over the years to take note of trends and colors as they run in cycles. I try to avoid too trendy fabrics, but collect unusual colors because I do a lot of applique. I do have one rule that's saved me a lot of money, I use the same criteria for clearance fabrics as I do for regular priced fabrics. Just because it's cheap is no reason to buy something you don't love or need.