Having a good musical ear, yet with very weak sight reading skills, I'm always searching for good books that can teach common blues licks/runs on the piano, while also explaining the "why" of how it works. This book is perfect. It can be used for a variety of things to learn:
--Licks/runs...there are hundreds of examples of great sounding, commonly used runs (as opposed to other books, whose runs can sound very un-creative or cheesy). Each run is usually only a few measures long, easy to pick up, and the book teaches you a great deal of different sounding ones in all the various styles of blues (boogie woogie, n. orleans, funky, jazzy, gospel, etc).
--Left hand bass...while only a few pages long, this section is flawlessly explained in a clear, straightforward manner. Harrison covers about 15 major (and fairly easy to pick up) left hand bass teqniques covering all the major blues styles. While it took a lot of practice to get all of them down pat, they have increased my playing monumentally. He also teaches you to always be mixing them to have variation in your bass.
--The "By Ear" element...unlike MANY other books, Mark Harrison's included CD is a god send. If you're like me and suck at sight reading, this cd is a blessing. The examples are short enough that once you can pick out the general notes, all you have to do is pop in the cd and hear clearly played note for note examples of what is on the page. I've found that hearing it cements the sound and timing of it in my head, making it easier to play, and also allows you to tinker and improv off the examples he gives you.
--Great summation and lead from basic to complex...the book incorporates more and more licks as it goes on, and covers more and more styles. By the end, when your listening to full 2-3 page blues pieces (the cd gives two tracks each for these; slow solo piano, and a faster one with a backing band), you can really get a feel for how all these runs are simply tools at your disposal to fit any given blues progression. Also great is that Harrison doesn't teach the very beginning licks as forgettable "step 1" sounding fodder...the licks sound great from the beginning by themselves, but are also used as building blocks to form more complex runs and comping later on.
This book is an absolute treasure trove of blues ideas, and a huge reason for my playing having increased so much over the past year. Mark Harrison's Smooth Jazz book is also good (it has a lot of great explanations for jazz chord voicings) but this book, and his "Jazz-Blues" book, are the two to go out and get immediately if you want concrete results without having the theory bog you down.