Dr. John Gottman has been studying the interactions of married couples for about two decades in his lab in Washington state. In this book, he compiles his best advice for what skills and habits are most useful to make a marriage work. He points out that most books on marriage will point out what not to do, and unlearning bad habits, which are certainly helpful, but without good habits to replace them with, progress can be difficult. He also states that communication, while valuable to any married couple, is not a magical talisman that will remove all problems from the marriage.
Some of his advice is a little more gendered than I'd like, and he certainly has quite an ego. Also, this books is written for heterosexual couples, but most of the advice is certainly applicable to any relationship. In fact, I know a few families who could use this book outside of marital relationships all together.
This book is also not a magical talisman for fixing any marriage, but I did find the exercises in it to be realistic and potentially helpful. He addresses a wide range of possible issues, their causes, and even accepts different levels of success. He also acknowledges that not all problems are solvable, but that marriages can survive unsolvable problems in many cases.
I will probably be keeping a copy of this book around, to plan premarital counseling sessions with and to loan out.