Line work defines the negative and positive space. I have always loved the contrast of a single line against a light colored ground. Charcoal, ink, pen or an HB pencil all have their own sexy character that can be used to add emotion to the subject.
I tend to use a Micron .03 or .08 for my sketchbook because i like the texture i can get by scribbling against the clean, sharp line work you can create. For larger pieces i tend to use charcoal or conte crayon.
