If you want a dead-tree reference set, the two-book collection
Wiring 12 Volts for Ample Power and
Living on 12 Volts with Ample Power will provide enough information to take you from no knowledge to expert. Not great literature, but pretty readable. And if you go to this section of the Ample Power website:
http://www.amplepower.com/primer/index.html
you can get free access to a number of short but useful articles.
Another book,
Managing 12 Volts: How to Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems, authored by Harold Barre, is also a good resource. It's widely available.