If you want to find and fix usability problems in your web site, the bad news is that finding them on your own is extremely difficult. You'll overlook massive show-stoppers because you know how the site is meant to work.
The good news is that usability testing, getting someone else to use your web site while you watch them, is very easy and extremely informative.
In this short, encouraging book, Steve Krug explains what you have to do in his wonderfully approachable style. In
Don't Make Me Think!: A Common Sense Approach to Web Usability, he zeroed on in the really important points about web site usability. In this new book, he's done it again with usability testing. It's boiled down to the essence of an approach that anyone could use, in 'a morning a month'.
Steve does not claim that this is a comprehensive manual for how to do any type of usability test. For that, he includes recommendations for further reading, such as
Handbook of Usability Testing: How to Plan, Design, and Conduct Effective Tests.
Not does he claim that his method is full-on, professional testing. In fact, he says: "If you can afford to hire a usability professional to do your testing for you, do it".
This book is for anyone who wants to make sure that their web site is easy to use, but doesn't have the budget for a professional.
Having said that, I am a usability consultant and I still found it worthwhile to read this book. If you've struggled to get clients to make the changes that you know are necessary, then here's an opportunity to pick up some ideas.
(Disclosure: Steve wrote the foreword to my book
Forms that Work: Designing Web Forms for Usability (Interactive Technologies))