For starters, I suggest reworking the hat to fit the piece's proportions better; it looks like he has Jabba the Hutt growing out of the back of his head. :P The outcropping of hair to our left is a bit strange as well, and could do with removal/change. A problem that pervades the piece is lack of detail in the shadowed areas; don't be afraid to use a darker color for things. Also, I'm not sure what his pose is and it might cause anatomy problems to do a human by chunks like this; sketch in the rest of his pose so we have more context for the form and pose of his upper body. While I'm on anatomy, the shield seems to hold itself, or else be held very awkwardly by a hidden arm. Generally I think Link straps his shield to his forearm so it faces to his right if he puts his arm at his side; work from that attachment into a better position/orientation of the shield.