Most of my stash consists of remnants (less than 1 yd and 50% off the sale prices), fabrics from the clearance section at JoAnns and FQs and yardage purchased at quilters garage sales. The few pieces of LQS fabrics I have were selected from the bargain bin. When I start a quilt, I try to select a focus fabric from my stash, and build on it from there. I'll pull stacks and stacks of remnants and pieces out of the drawers and audition them with the focus fabric. Often I can get the bulk of my selections from my stash, and then head to the store for a couple more to finish out the color palette.
It takes time and practice. I'm still practicing.- I've only been quilting since 2011, but have made nearly 40 quilts.