Sandi is right (go figure, right?) jk! The book is a good informational dump on why and how a marriage should work, ways to enhance it, etc. There are a few small sections that relate directly to MR that is already in crisis. But it is worth the read.
When Cadet posted the 'homework' in my first thread. I was a little overwhelmed and confused on which way to go. That 'homework' was crucial, and even more important that reading the DR book.
Sandi's rules, Validation, the LBS threads... One of the places I kind of screwed up (and didn't read), were some of sandi's posts on being a "doormat". A lot of times LBS Will Do Anything! for their spouses to come back and commit to the MR. However, I will warn against this, as I had to dig myself out of a hole or two when I became "doormat" material for my WW. It's easier to stop these things early on, than to let them happen, and have to claw your way out later.
Read the Homework, read other peoples threads, literally bury yourself in this as much as you can, but don't get stuck in information overload mode. Get the Knowledge you need (some people get stuck in this phase), but more importantly, find out how that knowledge relates directly to you and your sitch, and make a plan. Once you have a plan... take action and don't let fear/emotions change that plan.