Hi SamOne suggestion would be to look at the design of the face / head on a shape construction level. Much like you have done with the hair. The base shapes of the head, jaw, nose, eyes, ears, brow etc should all follow the same twitsed logic. At the moment its the same generic head with variations. Go more abstract first (silhouettes and shapes).
Check out Ruben's use of shape variation and silhouetteshttp://rubensblogpage.blogspot.com/2012/02/major-project-olivier-patissier-initial.html