Although there's nothing new here this a nice collection of disparate hints :good:
For anyone who hasn't learned to draw from books, breaking things down into basic shapes and showing the angle between one element and another is one of the classic teaching techniques, making it easier to notice* and remember key shapes, important landmarks and relationships.
As Tim says in the title this is also good for sculpting - that basic breakdown of the head into an ovoid or egg shape for the cranium with a projection below that for the face and jaw is one of the ways to begin sculpting a head from scratch.
Just to point out something in relation to the heads, most of the eyelines here are a little high. This isn't a big deal for more cartoony styles but bear it in mind if you're drawing or sculpting more realistically; it's more common that the eyeline is about halfway up the head measuring from the bottom of the jaw to the crown of the skull (not the top of the forehead).
*It's amazing how commonly we don't notice some things, such as the tilted axis of the ear. People just don't normally look that closely!
Einion