Start by breaking it down to simple geometric shapes.
A sphere for the skull with a vertical guideline for the direction it's facing and a horizontal line for where its eyes are resting.
From there, add a simple rectangular prism to shape its mouth, and you can just add in all of the details from there.
I realize it's not the style you're attempting, but the principal is the same regardless. You can change the shapes to suit your aesthetic, but if you want to be able to move its head effectively, this works pretty well.
Hope that helps. : ]