The most important quality of any hacker is desire and drivean itch to scratch, and the determination to scratch it. This book provided a tour of key parts of the kernel, discussing interfaces, data structures, algorithms, and rationale. It provided an insider's view of the kernel, in a practical fashion, to satisfy your curiosity or get you off the ground running in your kernel endeavors.
As I have said before, however, the only way to start is by reading and writing code. Linux provides a community that not only allows but also encourages both activities, whatever your pursuit, so get on that!