It would be difficult to recommend only one book to read in the field of personal development, but this is always the one I recommend people to start with. Written in a way that allows people from all walks of life to learn more about personal development, it teaches fundamental strategies and applies them in so many different ways that each becomes ingrained into your mindset as a result.
Covey is one of the most referenced authors for time management, and this book introduces you to the concepts of importance and urgency and will give you a clear way to prioritise everything you do.