If you think so....
The shading seems a little off. It looks like the lightsource is in the top left corner,
but some shadows are missing, like right side of the nose, right from the mouth.
It also lacks color variation, large areas are unicolor, especially the hair and the skin.
I'm no real artist, those are just things I kept from art class. But from my experience in the modelling section, you'll probably ignore my post.
Edit: Oh and if you expect serious tips, saying into which art direction you want to go (realistic, cartoon, anime'ish) helps a lot.