I spend a great deal of my time explaining the structure of the human head to people.
So much so, that when I find myself with nothing to do, I end up drawing little heads from all kinds of different angles.
That's where this sketch came from. I'd been lecturing about how to draw a head turn in my 2D animation class.
I'm tempted to draw up some kind of hand-out that illustrates the key moments and structure of the head as it turns but my fear is that, in doing so, I'll encourage my students to just mimic my style and approach... And, in my opinion, that's the worst thing an art teacher can do.
Instead, do what I did, and study life. Mother nature is a much better artist than I am.