I usually start out by finding one fabric I love take it home and look for a pattern then cut a scrap and go looking for fabrics that match it.That is why I have such a big stash, I never find a pattern or other fabrics to go with it. Sometimes I am lucky and the fabrics that go with it are all there and I buy them all together. I am lucky that I have always had an eye for color and have so much fun matching them up. When I first started quilting I would draw out the pattern and color it in with different colors until I found the combination I wanted for that pattern and then went shopping for fabrics with those colors. Study photos of quilts and see what others have used. It will help you learn what fabrics and colors compliment each other.