Based on several responses I received on a recent post of mine on visual thinking and drawing, I copied several images out of one of my sketchbooks to provide examples. In each of the drawings, I was working to record what I see and also think through the structure of and details of the subject. Well-designed organizations, structures, and systems will have elements of the whole in the details.
The best advice I can give you to develop your drawing skills is to draw often; relax and keep your mind loose and flexible; remember that your drawing doesn't need to be perfect; and keep your pen or pencil moving over the paper. Your drawing should evolve as additional layers of information are added.