I know, a question like this could spawn a debate into the next century. Being a self-taught artist, I often wonder about this question a lot. Many times I find myself just playing around with techniques. Or I have some object that I really want to use and I build everything else around that. I hate to admit that there is hardly any planning that goes into many of my pieces.
But, because my goal is to build an art career, I want to break myself of these habits. I've heard over and over again that successful people do the things that others don't want to do. Could this also be true for great art? I believe so. Great art takes planning and some understanding of color and composition. A commitment to an art career is a commitment to lifelong learning and experimentation. I have no problem experimenting and learning, but I have been known to be just a little impatient. Needless to say, I have much work to do in this area!
What I've been looking at:
A great introductory article on color theory at emptyeasel.com
How to create a body of work at about.com