Well, considering how lazy my method was a couple weeks ago, I decided to ramp it up and use my full-on illustration skills to make it look as best as I can. Getting good reference images helps a lot. Unfortunately, the characters and environments I'm painting don't necessarily exist, so I break out Blender, my preferred 3D modeling package and throw together a 3D mockup. I'll pose characters, set up lighting, and figure out my camera angles. I can then make a render of the scene to get a good idea for shading and color.
This, for example, is the mockup I just made today for the next scene I'm working on.
This horrific mess is a collection of pose and material lighting tests for a painting of my character I did earlier this year.
After I've got enough render tests to really understand how things will be lit, it's really just a matter of painting it. I've found that I often don't need to do these 3D studies as I get more practice. I tend to reserve the 3D reference for scenes with unusual perspective or lighting.