okay.
general formal stuff:
i dragged his head up a couple pixels. The head covers most of his torso, but you probably need to draw his abdomen. As is, it's not clear how the legs connect up.
-negative space is handy: break the arms apart from the torso.
-I grew up the hands and feet. Big huge hands is probably just personal preference, but he really does need huge feet to hold up that much mass. Think about weight and balance when drawing legs.
-i'm not really an anatomy guy, so the muscles are pretty off, I just sort of guessed it out. I usually check this stuff against a book, or someone who know's what they're doing.
contrast:
basically, just try to avoid using the same colours in any areas that overlap. If this is a lone piece (not for a game or something) you could mess with the light source until it works out right, or sometimes you can just cheat, so long as it doesn't make it look wrong, just chuck in more colours to break it up. I think the black I added around his ears and the far side of his face is probably cheating, but it doesn't look too wrong to me. Another example, I wouldn't use the same colours on his left arm and left leg, because you'd lose track of what's what.
If you're going to do it this way, probably you need more shadow tones.
Apart from that, you want highlights on areas that you want to stand out. I've focused them mostly on his arms and eyebrows, but if you wanted to shift focus to teeth or whatever else, bright hilights there would probably be the way to go.
