You could warp the logo a bit on the shirt so it is more wavy.
Add in individual strand of hair for the beard, may help
Start drawing the highlight and shadow paths for the face, nose, mouth and eyes. Might as well do the shirt as well.
lighten the one corner on the hat a bit.
Over all I do like how it is coming though. Keep it up. (remember my suggestions are just that suggestions, it is the artist that is the final judge of the piece)
