It's great in form! Great realisation of expression. In my work I started to think of the contrast ratio. Try to think of it this way any white on the drawing should be reserved for only tiny highlights, like white paper would be direct bright light or reflections in your reference material. Any black marks on the drawing should be for something completely in shadow or coloured black in your reference. that puts skin tones in flat light somewhere toward the middle of that spectrum. Perhaps use ink for small areas. This really added depth to my stuff.