The first thing I tell people is to get the book and actually read it:
It's become vogue to act the part of expert before acquiring the knowledge. My mentality is that I'm a lifelong student. Plus, the game is constantly evolving, so the "expert" moniker is an unhittable target. You're always learning. If you want to break away from talk radio bullshit, this book is the place to start.
Me, personally? I'm more into watching the edges (corners, receivers) for two reasons:
A) Most individual matchups happen outside, and I don't need a high football IQ to enjoy individual matchups.
B) Analytics strongly suggest that you build teams on the edges.
The book also has amazing resources for charting games (formation tendencies, run/pass breakdown), a scouting template for draft prospects, a glossery of football terminology (if you have no idea what "running behind your pads" meant, this book explains), and just general, fascinating nuggets on the life of an NFL coach (how the work week is structured, for instance).
Get the book, read the book. There's no shortcut. Do the fucking work.