Please use references if practicing. This is something really quick. Notice how the back skull is too small.
The eye thing helped me a bit (I can't get the source though, but it seems to be from a comic making book)... There are a lot of tips on drawing side portraits... and for some reason, people are finding my old ass tutorials, I decided to update my dusty dA with some times I gathered. Work hard, practice, experiment! Thanks for visiting!