ok.. not much to it, but here's my PROcess.. because all pro's have one, HA! I R dumb.
First I get some vicious line going, or not, doesn't really matter. Just something.
Then, I put some value on it using multiply layer(s). Doesn't have to have local value yet, just has to have a basic feel of lighting. The tighter the value, the faster the color goes down. This is just for this lame drawing, but for something bigger, i would do the value of the entire illustration using various brushes and whatnot. Generally, for basic rendering I painter 9.5, with the fine point pen tool (to lay flat value) then blend as needed with the just add water blender. Kind of boring, but it works for me. Easy to delineate between cast and form shadow with sharp edges, so not everything is soft. I'm sure other brushes are faster, but there's always time for experimentation later. This gets my job done.
Next is the fun part, I use a combination of overlay layers and default. With the basic value and light pattern set, you can really just go crazy with trying different colors and whatnot. I put down a basic fill of a color, to get an idea of mood or color. That way, when you put other colors down, you can use a smooth brush or just add water to blend it if needed. The local value can be done in this step because overlays change the overall value range, which i like. Funny fun fun.
Then, tada, you add a background around them if you want to bring em out. Some little temperature changes to highlights, blah blah blah academy teachings, blah. Airbrush works nice and i like the splatter air brush for adding pimples and whatnot. That's it! I should try to find a simpler process..