We designed this book to be useful to end-users, systems administrators, and developers who interact with RT on an occasional or regular basis.
If you're an end user
Start off with Chapter 1 to learn about ticketing systems. Then skip forward to Chapter 3 to find out how to use RT's web interface. If you're comfortable getting things done with command-line interfaces, read Chapter 4 to see how to use and automate RT with rt. After that, pick and choose whatever sounds interesting.
If you're a systems administrator
Chapter 1 will give you a background in ticketing systems. Chapter 2 helps you get set up with a live RT instance. After that, jump ahead to Chapter 5 for help setting up users, groups, queues, and access control. Chapter 7 is filled with suggestions for potential uses of RT inside your organization. Once you have RT up and running, chapters 3 and 4 will help with day to day interaction and should make a good guide to help your users get comfortable working with RT on their own.
Once RT is up and running, you should check out the rest of the book, which focuses on development and customization.
If you're a developer
If you're a developer, it probably makes the most sense to read this book straight through before you start hacking. The first section focuses on getting a system up and running. The second section talks about basic customization and configuration. The third section focuses on how RT's code and database are put together.
If you're chomping at the bit to get started, read Chapter 2 to find out the basics of installation, then Chapter 10 to learn a few tricks that will make your development process much smoother. Chapters 9 and 10 will explain how everything fits together.