There's a problem I have, that I noticed so far, and it's that I lack ability when it comes to mouths, mostly feminines haha...
Just a matter of practice really.
Find a tutorial / book on drawing human faces.
There are a few here I believe:
http://conceptart.org/forums/forumdisplay.php?f=42Another thing I'm a bit confused about, was what you said so far, on regards the putting up two highly contrasted shades together... do you mean using two colors instead of 3? (bright - regular - dark). And do you have an example image that I can see so I can make sure that I really know I'm on the right track...? Thanks, and sorry for being a pain over these, I'll appreciate if you can show me that image.
I was worried about that not being very clear. Unfortunately I don't know the actual term for what I was trying to convey, maybe there isn't one.
When I look at your picture I see a lot of this:
A blended look, no sharp contrast. There are very few instances where you want to do that, especially in small scale pixel art.
You show depth through contrast, less contrast = less depth. More contrast = more depth.
If you look at your picture there is very little depth because you smooth everything out with the use of intermediary colors. On the armor this is ok because it's a smooth, mostly uniform, surface with a low curvature. On the nose and around the eyes it makes these features look flat.
Take a look at the nose on your image:
Notice the shadow ( brownish color ). You surrounded the brown shadow with the yellowish-grey intermediary color, negating any real contrast on what should be a highly defined part of the body.
Here is my edit ( on the right ):
Notice the nose again. I put the brown shadow color directly under the light skin color creating a high contrast and thus indication of a sharp angle, which makes it look like there is a protrusion on the face ( which we refer to as a nose ).
Well that's about as good as I can explain it. I hope that helps.