One of my favorite books, and the one that has probably influenced me the most as far as my thinking, is The Yellow Emperor's Classic of Medicine. http://www.amazon.com/The-Yellow-Emperors-Classic-Medicine/dp/1570620806
This book talks about the way we must live our lives in order to stay in balance. For example, you have to carefully guard your health in the winter time, because you have the least amount of qi then. I really felt I did not do this well enough when I kept getting sick this winter, and that's something I am trying to work on.