http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
This will give an overview of how Drupal outputs content, and how to design around that visually, as well as an overview of turning the design into a theme. Less of a comprehensive, "these are all the hooks you'll ever have to deal with" volume, and more of a "this is how to understand how Drupal works so you know what you're applying the visuals to" thing.
Electronic reproduction. Boston, MA : Safari, Available via World Wide Web. 2011.