Drawing of the face, for example! The eyes, nose, muzzle, whatever on the character's face!

Seconded. The face is one of, if not THE most important part of a piece of character art. Make the face look awkward, and that's the first thing people will ridicule about it. Facial structure, the anatomy of expressions and how to use them, and the obvious difficult subject of muzzle foreshortening would all be very good subjects for an instructional video.

I love the jumping on the bed in the first vid XD