Your lighting should follow the contours of the guys body and hat. They shouldnt ever contradict or run-over the contours. Like the hat seems to bow, but the light tone is just straight, and your darkest tone borders the entire hat. On the body there are ribs, but their expression is absent in the brightest tone.
Also, avoid outlining things. On the hat and the body your darkest tone outlines the entire shape. You dont need to do that.
Would you like me to do an edit on your piece to show you what I mean?