Such a nice drawing. Nothing like the trademark mechanical hands.
I think your coloring is quite good myself---as with using Photoshop, I think the best advice to give is practice and try new stuff. That's the best way to learn.
The mouth thing is spot on, actually. Criticism: It extends too far, seemingly past the chin. I pulled up some random anime styled pictures to confirm/disprove this. Comparison, go:
At any rate, it doesn't look bad enough that you notice it; you have to look for it. It looks a little awkward, and could easily be fixed, I believe. Etc~