For many years now the work of Mark Bannerman has been a great inspiration to me. His technique in painting faces was instrumental in me developing my skills as a figure painter, however I still need to learn when to stop. Since I tend to over paint the faces. Here are a list of links to his articles on painting 1/35th faces in oil colours orginally published on the Missing Lynx website.
Painting 1/35th heads in 8 steps
"The Bannerman Way"
"The Bannerman Way Part 2"
Painting figures adding details
Painting Asian faces
Painting Black / African faces
All by Mark Bannerman