I enjoy making these handouts for my classes to help explain specific concepts. The one on the illustrates starting a portrait with the "basic frame" and working the detail over this. The handout on the right discusses a specific feature, the eye:
Also, I was taught the concept of the "basic frame" from my teacher Arthur Wang at Columbus College of Art and Design. He is a great draughtsman and teacher and I took his class for a few years. His website is here.