When I haven't been working on freelance web work, I've done a few environment concepts for an open source game. Nothing's really set in stone yet so I've just been playing with mood, lighting, and shape.
When I don't know what I want to create, and I want to "sculpt" painted shapes into something that I can further refine, I use a digital version of a Grey PrismaColor marker. When I know what I want to create, when I have something fairly solid in my head, I like to use the mechanics of drawing and draw-through methods to create what's in my head.
Until this painting though, I haven't been able to apply typical drawing mechanics to a digital canvas. The size of your canvas has to be the right size relative to your brush. That can be hard to figure out.
I also had some preconceived notions about actually drawing when I thought I should be painting. I know differently now. No matter how much you paint, the mechanics of drawing are VERY important. You might be painting your heart out but if you don't have the drawing foundation to back it up you'll be lost.
When I say the "mechanics of drawing", I'm not talking about actually using a physical or digital pencil, I'm referring to the skills you learn from drawing. Seeing the right way, creating shape, and perspective.
I think I'm starting to get it, and can't wait to do more.I need to learn how to refine less though, and just use large brushes, value, and color to illustrate my ideas.
I really like the mountains in the background :P