I have only been quilting since past summer; but I find that I choose a pattern I see or buy a pattern I like and then proceed to picking out the colours that I think complement each other. Of course, it depends on where the quilt will be used; that determines colours as well.
I have only bought one kit (Tag Sale by Moda) cz my hubby fell in love with it and gave to dd for Christmas. It turned out great.
It is so much fun; I can't remember what I did before quilting! :)