I don't over analyze it. I usually spot a fabric that just speaks to me, then I try to coordinate or contrast with that. My LQS used to have a teacher that had a great eye. I always liked to get her perspective on my choices. She usually pointed out that perhaps a white was too white for the other fabrics, or that a green I had picked out to go with a bunch of browns and beiges were too monochromatic, suggesting a red, that turned out making the quilt pop! I usually try to pick out various colors in the main fabric, and gravitate towards them.