I have been asked to do a tutorial before..this is pretty close without the marker details..so i thought i would share for those that are interested..
1. Layout sketch/idea sketch
2. Tight sketch cleaned up and ready for coloring
3. First layer of under drawing using various shades of gray(warmer tones). As well has the cool under shadows on the face. Nice and tight in detail as this is the main focus.
4. background under drawing. Not as tight to give a slight depth of field effect. Nor are the shadows as dark as the foreground subject. (cooler gray tones)
5. color layer blended on top of the under drawing.
6. final piece after it has had a round in Photoshop for the finishing touches.