When I first began quilting, I worked on my stash faithfully. At first, I picked an area at a time-novelties, baby fabrics, 1930s, Civil War, florals, solids and textures, black, white and cream tone on tone. Then I started on Christmas, Autumn, Halloween, Red and White, Black and White, etc. I watch for fabrics on sale to buy "quilting sets." Like someone else said, I try to work within a suite of primary fabrics of one line for quilts. I can add solids and textures later.
When buying fabric yardage, I usually buy 3-4 yards of the primary design. If I think it will be used for a small project; 1-1/2 yards. Solids and tone on tone-2-3 yards, sometimes more if the price is fantastic.
This was so hard for me in the beginning because I had no concept of how much yardage would be needed for anything! It's getting easier now than I sew more often.