Today, I wanted to share a technique that i've started using thats helping me to create 2D face sketches more usable for Rigging. I'm not a professional Designer or Modeler but hope it is helpful.
1. first I created a 2D concept idea example(s) with some rough poses.
2. in ZBrush I sketched at the concept not paying too much attention to exact likeness because the design could change before making the topology for rigging.
Damian Standard Brush --- I used for indents and adding big changes like eye socket divet and eyebrows.
Pinch --- I used for getting more pronounced crease like getting the lips to look more closed.
Move Topological --- I used for sculpting silhouette like head, jaw, bending ears
flatten -- I used to get flat side of cheek, and make front of brow flat
clay -- I used like Damian Standard but for very small changes
also, when I ran out of room to make indentation I used (ctrl+d) to add more subdivisions.
And when I couldn't smooth a corner because too many faces (I went into geometry and lower divisions and smoothed there instead)
3. I imported the ZBrush sketch into Maya and took side, front, and 3/4 screenshot.
4. in Photoshop I imported the screenshots from 3. and lowered opacity.
5. I sketched construction shapes in light blue thinking about roughly following 3D ZBrush sketch.
6. I drew over the blue layer made in 5. with two darker layers. The first darker layer I used for overall landmarks. The second I used sparingly to close shapes.
Daniel Williams's ZBrush tutorials (pointpusher dot com)
Ben Caldwell's Fantasy Cartooning