First, I start with a basic sketch--I try to get the proportions right, but it's never going to be perfect:
Then I try to clean up the sketch to look more like the person I'm trying to draw:
Here, I've filled in the skin, and started adding depth with a darker skin tone in the shadows. I've also mostly laid in the hair, starting light and adding dark on top for depth and texture:
Here's everything but the highlights (I have yet to rub off the masking fluid, or to add white paint in the very bright areas):
And the final product:
Anyway, hope that's interesting for people.