There are some excellent free downloadable pdf books on face and figure drawing here, ACEGUY:
http://illustrationage.com/2013/04/0...ion-downloads/
They're public domain "how to" books by Andrew Loomis, a real life Don Draper (ie 60s commercial artist/advertising man) and include some great sections on anatomy, expression, figure pose and balance, drawing multiple characters in perspective and so on. All very relevant to superheroes and narrative comics in general.