Contrast is highly inconsistent: extreme on the left side of the face, very low on the right side, non existent in the hair and beard.
Think of a light source(s) and try to guess how it would look. Better, test a light source on you and see what it does in the mirror!
Linework could improve: it's a bit jaggy in some places, and these inside outlines are probably not all needed.
Are you using a ref picture? If so, please show; if not, find one(s)!
