The lighting on this head is kind of all over. On the top it is kind of stating that light is coming from above, but on the sides and stuff, it shows that it is coming from the bottom or some sort. So chose where the lighting is then work from there, dark spots should be on the bottom and light spots should be on the top if light is coming from the top. Also fix the middle crease. A good technique to do (for lighting) is make the background a demon type color, not totally black of course, then you will see how the shading will go (when you are in sketching form) Or just get a light soft brush, and keep it on a separate layer and just brush where you want your light to come in. So you always remember Hope this helps. And turning out to be a nice head.