Got inspired by some other dude to have a go at the avatar, here's another attempt. cant find my eraser For some reason ipod photos always go sideways
You need to look at proportions more closely. The arm/hand is way out, and the top of the head and neck need further work.
Try lessening the amount of lines around the face. It makes him look really old which he isn't, and his anger look more like laughable rage. It's really good though!