I had taken a brief marriage improvement class with my husband where we were introduced to Gottman's "Four Horsemen of the Apocalypse" idea; this is the concept that four behaviors are major predictors of success or failure of a marriage. They are: withdrawal (stonewalling),criticism, contempt and defensiveness. While it's good to know what to avoid, it's better to know what to do. That's where the "Seven Principles" come in; instead of just warning you away from negative behaviors, the book helps you identify positive behaviors that can strengthen your marriage.
When I saw this book at the library, I knew I had to pick it up and give it a read. One of my favorite parts of the book were the case studies, where he puts the principles into story form with a variety of couples, and shows how these can work in a real life situation. I find that really helpful. If you're a slow reader, you may enjoy listening to it as a book on CD instead.