Fitness books have been a great source of information on exercise routines, proper diets, recuperation suggestions, and giving insight into new exercises. I have found that I tend to pick bits and pieces from a few different books while also finding information on the web. Books are a nice way to readily have the information available and have all of the information in a more structured format.
Fitness book considerations are not a lot different than what you would consider in buying a high quality running or cycling book. I find fitness books to have larger variations of topics and content, so be specific in what exactly you expect out of the book before you put down money on a book that may not provide what you are looking for.
Some fitness books can be a great source of exercise routines or at least details on exercises and plans to help create your own routine. Understanding the nuances of a balanced exercise, proper techniques and diet can go a long way.
Considerations: