I'm slightly new here. I'm mainly a writer, but I've been making adventure games under cover. I "painted" this to visualize one of my characters. Critique it as much as you like.
(http://www.geocities.com/thefewer2003/stormarmfinal.jpg)
Remmington Stormarm
You should look into how do draw proportionate faces. You can exaggerate it to make it caricaturized, but still follow basic rules of proportions.
Here's a quick example I drew in Paint: (sorry, I'm not much of an artist)
(http://www.gregjazz.com/upload/characterface.jpg)
As Gregjazz said; you should check out some books and study how to draw a face. It will help you more on the long run.
I tried to do a quick overpaint of your drawing.
(http://www.blueangel.dk/AGS/overpaint1.jpg)
This shows you the changes I made:
(http://www.blueangel.dk/AGS/overpaint2.jpg)
I'm no expert myself when it comes to draw humans, so I'm aware that there may be flaws in it. But hopefully you can use it as a guideline or something ;)