Go to your quilt store. Pick out a fabulous Big Print with lots of colors (ones you love, or ones that you want to design your quilt around). Like this one I found.
Then you can pick out fabrics to coordinate with it that have those same colors, or you feel will coordinate well with the colors in that fabric. You don't even have to use the first fabric you pick out, you can just use it find fabrics that will go together.
Another cool thing that fabric companies do now is print color dots along the selvage of the fabric. It shows all the colors that were used in that particular print and you can use the dots to find coordinates.
Now wasn't that easy??