The face angle is a bit off so I adjusted it while trying to keep the features as much as possible. The eye on the left should be more foreshorten. Now for the hair, I do think you should try to think of it as big 3D shapes then slowly add more and more details when you have the bigger shapes down. Think of it like sculpting clay basically. So, basically any planes of a 3D shape facing the light is lighter and anything facing away is darker. All solid forms tend to cast a shadow, your original work has that concept but you just need to use sharper and clearer shapes to show the cast shadows, ie. the cast shadows on the face by the hair. If it gets too complicated for non-focal point of the hair, like the back layers, you can use shadow shapes to imply separate strands without needing to fully visualise them as 3D shapes. Also think of the hair as 3D shapes stacking on 3D shapes, this can make the hair feel more layered. At the end you can add more details by adding small strands. I hope that helps and good luck :D.

