When you've worked in a quilt shop for 16 years, you get to know all the different types of fabrics. The easiest way to choose fabrics is to stay within a fabric line. Each fabric line should have large scale, medium scale and small scale prints. They should also have light, medium and dark fabrics, and some that "read a solid." It's a good idea to use all 7 of these basic design elements in your quilt.
Then as a quilt shop employee puts fabrics away, she will come to know different fabric "families." These could be Civil War, 30's Repos, brights, batiks, dark and dirty, soft and sweet, and they may include your favorite fabric designers. Then there are the basics, and the leftovers that make up the color wall.
If you can start with a "focus print," then you can choose at least 6 prints that match it.