There are many different ways to start a portrait drawing this video will show two examples. There are many more approaches and different mediums to accomplish the work. I could have worked longer finishing, but my goal was to show the procedure. Hope this video is helpful.
These two videos are about value and shading. The first part is in lecture format and the second video is a demonstration of shading
This Video is about Value and how it works
This video is a demonstration on shading using a Sphere form.