Are you using a tablet, if you're not you should probably get one. A bamboo is a great starting tablet only about 80- 120 dollars. Well if you do then don't bother with that shit I said.

Anyway on the art it's alright, the neck lines and the face lines are a little stiff but it's good. Did you draw in MS Paint? Because it looks like you did with the bit of white where you have coloured.

If you are you should probably get Photoshop, Flash, Pencil... there is a lot more these are just off the top of my head.
Also Jack's shirt and jacket look odd.