Dave & The Process

Here is the process I use when painting my digital portraits.
First I lay down some color with a hard brush. This is just to map out the skin color before I put in the shadows and highlights. Next I smudge those colors together (I'm a sucker for the smudge tool). Also add a solid color for the background.
Next I add in the darker colors with a softer brush, and add just a little bit of the highlights.
Of course then I use the smudge tool again, and add in the lightest highlights.