If you've read my posts on the NFL you know that I'm a fan of the advanced statistics calculated and promulgated by the guys at Football Outsiders.
For the last few years I have picked up PDF versions of their Football Outsiders Almanac during the NFL preseason. It's a great read and gives good context for the upcoming season. I personally use it to prepare for the fantasy league that I play in, but I've never won a dime in that league so maybe you should take my advice with that in mind.
Anyway -- gratuitous plug here, I'm not getting a cut or anything -- Football Outsiders Almanac 2013 is now up for sale in PDF at the FO store and I'd encourage you to check it out.