Treat ZBrush like clay
Using clay sculpting techniques for ZBrush
Start with a skull
Cut in for lips
Add a clay ball to begin sculpting the nose.
Add malar fat and other fat pads to fill in the face.
Add cylinders for the top eyelids
Add cylinders for the bottom eyelids
Smooth out the seams for the sculpture
Add zygomatic major
Refine the sculpture