your perspective seems a bit off.
(often times i find it helpful as a 3d artist to create a quick mock up in 3d space when i have a perspective heavy work of art... )
you can probably achieve something similar by messing around in google sketch up to improve perspective understanding.
somethings a bit odd contrast wise...
the eyes seem to be way too dark for the lighting... giving the feeling of eyes sinking into there socket.
and the hair is rather flat looking with the only shading appearing to be variations in color or definitions of strands....
but all in all its a good piece.
your anatomical understanding seems fine
best of luck to you! :)