There a re a few ways to paint an effective, realistic porttait in monotone.

In Part 1, We start you off with this one using just a single colour.

we look at the first steps of
Realism
Skin Texture
Using multiple erasers
Materials
Using Transparent Base
How to make your colours more transparent
Contrast
Depth of field and focus

This tutorial is an ideal step to creating your first realistic monotone portrait.