I don't fell qualified to do crits anymore, but I will anyways...
I don't even know where to start, it's very painful

A Persons face, You can google this easily, anywhere...always use referances..DO IT or Segata sanshiro will hurt you.

My avatar "portrait", I don't like it much, but it still works. Use it to base colors off of, I wouldn't recommend using it for anything else except anatomy. Forget anti-aliasing, there is none. Notice dithering the the background
http://library.thinkquest.org/C0126120/ethan.jpghttp://www.cs.princeton.edu/~chazelle/pics/teenager.jpgpallete:
The pallete for skin is all yellows, it's all same-ish. Are you sure your not related to The Simpsons? Base the skin off of a tan color and stay away from yellows. Make a larger contrast between colors, don't be afraid to add contrast.
You have greens in there, I'm not sure why, it just looks bad on the face..
Anatomy:
If your holding your neck with both arms raised up, then it doesn't read well enough for me to tell, to me it looks like it's all one entire piece of your body, if this is not the case, however: People's necks don't bulge or curve to meet the shoulders, think of the neck as a skinny cylinder attached to the top of the torso.
The top of your head appears to be missing tiny chunks of pixels from it. this is due to sloppy lines (below). It's also too small or skinny to looks like the human cranium.
The hair, frankly, looks like a blonde wig due to how you've shaded the face and isolated the hair so much.
Aliasing:
On the aliasing side of things, to be blunt: EVERYthing on this is an aliased nightmare, everything is blockey and/or jagged and needs Anti-alias real real bad.
Overall lines:
The line-work is a jagged mess, and just looks thrown together in about 15-30 minutes or so and was never cleaned up. Make the lines follow contours smoothy and make sure they don't turn jagged and super blocky because a pixel was supposed to be there or wasn't.