Draw the lines where his eyes, nose, and mouth will go. These lines should be CURVED not straight because his face is not 2D. Draw the basic outline of his ear too.
Sketch in the outlines of his nose, eyes and the edge of his face. His eyes are huge and oddly shaped so you might want to look at a picture of them from the movie to help you out.
Sketch in his mouth and teeth LIGHTLY. His mouth really makes it look like him, so do a good job. I had to erase and redraw a ton of times, so be prepared. I also mapped out where the shadowy parts of his face are.
Start shading in his eyes and nose as well as his mouth. Sketch in his hair and shoulders as well. Do these lightly so you can erase if you need too.
Shade in the weird patterns on his forehead and face. Start shading in the rest of his head. Using little circles to shade or using the side of your pencil is good.
Shade in his hair and ear and overall finish all that shading stuff up.
Finishing touches. Darken up the shadows and make those weird light dots on his face. A kneaded eraser is good for those.