I would suggest you do a google search for a color wheel. Print it out (I lamanented mine). When you select a color use your wheel the colors on either side of your color are complimentary. The colors diagonally across from your color on the wheel are contrast complimentary colors (like red and green contrast complimentary colors) I like to have contrast in my quilts I think those colors groupings make t pop.
Another tip I like is using the selevage strip to pick other colors for your quilt. If you find a fabric with a print with more than 2 colors along the selevage are color marks of all the colors in the fabrics. It helps me pick out other colors for the quilt.