Here were some suggestions from a friend Chris Solarski:
"These pencil/drawings drawings I prefer to your marker drawings, without being able to describe why. They have more 'life' to them, whether that means anything to you!
I especially like the first and last drawings, in which you've captured an individual character and, it seems, done something more than just copy the model.
To push your drawings a little further I'd suggest thinking more about how you use light and shadow to describe form. You have done this to some extent. However, in the case of the last drawing, if you'd visualised the face as a simple cube and decided the light is coming from the viewers left, this would reinforce the feeling of form by establishing the side of her face as being in light and the front, in shadow.
I'd also recommend making more use of construction lines.
Thanks CAS. I think I need to be in touch with making intelligent choices with light and shade as a tool rather than as a strict effect of nature, so that I can in choosing manupulate the form. It is a language that can tell one story or another with the very same form.
I think that I will try to use construction lines. All good suggestions!