Good start for your first attempt Elephantinc,
I'm wanting to try out some cartoon characters soon, got some other bits to do first though.
Some points I'd say:
Pull the cheeks back a touch, define the brow line first before doing the forehead, to make sure the size of it goes with the eyes and rest of the facial features. Pull the chin down slightly, thin out the neck a touch and flatten the sides of the head as a whole a little as it's looking a bit alien at the moment.Also the eyes are at too much of a diagonal angle, straighten them a touch.
Are you using image planes of the head, if not it'd definitely be worth sketching something to use or using photos for your first attempt, saying that the pros seem to use them all of the time too so probably something to think about (if you aren't using them)
Sorry for giving you so many crits, just trying to help. lol!
If you spend a lot of time on it I'm sure it'll come out looking cool!
Good luck with it!