16 Ways to Love Your Lover is an excellent relationship handbook. Its an easy introduction to the 16 temperaments and would be especially beneficial for those who's significant others are of a different temperament to themselves. Even though it is aimed at couples the principles of understanding/relating to others is very helpful. It gives practical everyday life advice, from communication to sex and money matters. The book gives short examples of couples which helps you to see the different temperaments in action and there are excellent graphs that can help you solve/understand differences or trouble spots between you both. Apart from all this, I also found it helpful in specifying my own needs and wants in a relationship. If you want to improve your relationships, or understand yourself better, its definitely worth a read.
While this book is generally on with its observations of general human behavior, it should in the relationship section, not psychology. Its pop-psych style of unsubstantiated examples doesn't provide much valuable information for you to learn from. It's an entertaining read, but when all is said and done, it's difficult for a reader with any knowledge of the MBTI to feel like they've learned anything worthwhile. If you want a book about relationship quirks, this is the one. Otherwise, look for something else.