I really have no idea when it comes to shading, but this is probably the best I've ever shaded anything without reference. I know it's still not right, but it's quite good for me.
I got really stuck with the hair. It kind of kills the image...
I look Laurel's advice and tweaked the lips a bit, though now that they are coloured I think the shape of the bottom lip could be a bit better... maybe slightly bigger or rounder?
Anyway, this is quite bland in comparison to Loish's work, but hey, I'm still learning! :D