When picking out fabric for a quilt, I usually start with my pattern. Wander around in the store until I find what I want for a focal, or primary fabric in the quilt. Will then move on from there. I usually end up carrying around bolts of fabric with me for what seems like hours sometimes. If you have difficulty trying to figure out coordinating colors, try using the dots on the selvage of your focal fabric...those are the individual colors used to make up that pattern/design.
I will also, lay out the bolts with the lesser fabrics hidden, so to speak, so I can get a sense of what the visual will be. Focal on top, an inch or two of next fabric and so on. Or how they are going to be used together to get a sense of how it looks together.