Your lighting seems to be off.
Use lighting to show shapes, not just where the light is coming from. Everything is going to be build out of 3d shapes, and each one has it's own lighting and shadows. Think of that when your shading.
Also, the hair seemed to be pillow shaded, meaning the light source looks like it's in the center.
Here's my edit:
For example I gave his cheek a light source, his nose, his brow, his upper lip. They all have their own lightsource.
You may want to add some more colors too, such as some shadows.