I pick my main fabric first, usually the busiest and most colorful. Then take a swatch with you everywhere you shop to match and blend other fabrics. Know your basic pattern pieces as well so you can decide whether the small ones work well with a large print, and vise versa. Just have fun with it and know that your creations is as right as it seems to you. No two of us see things the same way and you only need to please yourself or the person you are making it for. Have fun and enjoy the process.