1. I make outline from my reference picture at the new layer (above background layer). You can see my reference picture here. No detail outline is needed.
*Click image to enlarge
2. Make basic shape of the face, at the new layer, and place under the outline layer. I need the sharp edge, so I set the Brush Hardness: 100%.
3. You must choose shadow and highlight color, place in the new layer. Then, add some rough shadow (remember, each step, place it in the new layer, for facilitate when editing/ finishing). You can see my brush setting, here: Tutorial Basic Digital Painting, I always use that brush setting.
4. Make eyes and eyebrow. To make eyelash and eyebrow, I use this brush setting (F5): Shape dynamics, Control: pen pressure.
5. Add lips. I choose soft color here.
6. Add rough hair, no detail needed, this is just for basic hair shape.
7. Add face shadow and highlight.
8. Add hair shadow, I use "Charcoal brush", brush setting: Spacing 1%, Other dynamics: Opacity jitter & Flow jitter: Pen pressure.
*Click image for detail
9. Add hair highlight.