Idk

You did all right with the lips, if you want to make them more realistic and full you could shade a little more. Light shading on the upper lip that comes up from the opening of the mouth, and shaped as the lips would be shaped. Also light shading just below his lower lip. And I think the neck is a little thick, unless there is something around his neck.
Oh, and you can do a little shading in the dip below his nose and above his lips that most people may have. That could help, too. Show the shape of the dip.