The only advice I would give is to
love the fabric you're buying, not just like it. This applies even when it's cheap, on sale or 'too good to miss'
If you love it when you buy it, chances are it won't end up in the bottom of the bin or in that scrappy quilt.
You'll know you love it when the shop owner starts giving you odd looks while you're standing petting it, or worse, talking to it - ask me how I know