I believe color choice is everything. Pay attention to value change, a quilt must have light, medium & dark to be effective.
I was taught over 45 years ago, before all the fancy gadgets and fabrics were not out there.
Simply learn the color wheel and it's principles. There is alot of info on the web about color theory.
here is a link to a good explanation:
http://en.wikipedia.org/wiki/Color_theory
I first select my theme fabric, from there I select 2 colors, and working the value scale, find colors that will work. Background colors of white, neutral or black do not count as colors, they are the canvas that you work from.
I have always found this method the easiest, as the fabric designer has already done the hard work. They have created the color pallet.
If I am not sure of a color and if it will work, I make a sample block, and use mirrors to multiply it and see if the effect I am looking for is there. At this point if I don't like it, I've only wasted a small amount of time & fabric.
Hope this helps.