I'm an avid reader of instuctional guides. I have not been playing bass long at all but I can tell a good guide when I see one.
I have the Dummies guide to Bass and one that was put out by Bass Player magazine ( I think) however...
I cannot recommend enough the bass book printed in '07 by the Teach Yourself Visually people. (I think the publisher is Wiley).
This book is really, really good. Everything from tuning and care to slap 'n' pop but described very concisely, in plain english, with tons of high quality photos. As an afficionado of reference material I really enjoy reading this book. It has made lightbulbs go on over my head numerous times regarding topics that other books seemed to only hint at.
So, yeah. Teach Yourself Visually Bass Guitar.
Good luck!
