Here you can see how I work a bit.

This is drawn from setting up a skeleton with a light beneath it as a still life and drawing it from observation. I start out with an H2 Staedtler pencil (my favorite) and do large fluid strokes while holding the pencil sort of loosely like a paintbrush. Then once it's a loose sketch I work all over tightening the work up until it's an accurate contour line drawing. Then go in and add the shading. After shading I'll go in and work the details in and get it rendered to accurately match the bones.

Graphite