ey.
I think the essence of cartoony looking stuff is that everything is simplified. So IMO you shouldn't use too many colors — I think a lot of cartoons even only use one for skin most of the time. Also, from that, dithering should be avoided because besides creating a third color, it adds a detailed, textured feel to things.
Have you found out about Andrew Loomis's books yet? They help a lot with drawing figures and heads, and many people seem to leap very rapidly to awesome drawing skills from studying them. I haven't had that success and am still struggling with basics, but comparing my drawings from 2 years ago when I started with them and now there's still a lot of difference.
There's a note by ptoing on skin shading:
http://www.wayofthepixel.net/pixelation/index.php?topic=56.msg808#msg808I did an edit where I tried applying those and balls01's to your picture and exaggerated the shading some:
and then that one edited for less warm and less contrasting colors:
also, it's recommended to present images as PNG or GIF around here I think..