Try finding a fabric you like that has many colors. Then use that fabric and use it as a guide to pick out colors. Sometimes the fabric will You may decide that you will use the original fabric you chose in the quilt and as the border, or you may not use it at all.
You can also get a book on color for quilts. Certain color schemes work well...like blue and yellow, red and green, blue and green. The more you pick out colors for quilts, the easier it will get.