The number of books you can read about how to write books is practically unlimited. There's no way to read them all, and there's no reason to try. Here you have a list of books that have been recommended by other writers, and what they are most suited for:
On Writing - Stephen King
This book is part memoir, part inspiration for writers, part tough-love and solid advice. It's short and accessible, so it's a great place to start if you are just getting started or are trying to regain your footing as a writer.
Bird by Bird - Ann Lamott
Often heralded as "writers' therapy," this book is a funny set of inspiration and motivation for writers of all stripes. Not a balm for your mechanical issues, but more of a balm for your writing soul.
Save the Cat - Blake Snyder
Though touted as a book on screenplays (which it totally is), this is one of the best books on pacing and unraveling a story, period. If you've ever questioned what the three acts of a story are or how to know if you're keeping readers engaged, this is the book for you.
Writing Down The Bones - Natalie Goldberg
Like Lamott's book, this is more of an inspiration than anything else. Meant to help you "free the writer inside" and connect with the creative side of your personality, it's not really about the business or technical side of writing at all.
PoemCrazy - Susan G. Woolridge
Techniques and inspiration for creating poetry and recognizing it as more than the angst-riddled stuff you churned out in your teens.
Characters and Viewpoint - Orson Scott Card
A detailed outline of how to identify and create relateable characters. Card gives tips and exercises on how to craft these characters, all in an easy-to-read, easy-to-identify with voice.
How to Write Science Fiction and Fantasy - Orson Scott Card
Another accessible how-to-guide from Card, this gives tips on building and populating worlds other than our own. Speculative fiction writers face a set of unique challenges, and Card addresses them all.
The War of Art - Steven Pressfield
Applicable to all creative processes, this helps creators (writers) overcome the burdens of creative block and manage the technical aspects of their craft while still being true to the artistic drive that fuels the effort.
A Million Miles in a Thousand Years - Donald Miller
A psuedo-memoir crafted to better articulate the needs of a story. Miller deliberately set out to make his real life more like a story, and succeeded in understanding the ins and outs of creating characters, conflict, and setting.
Becoming a Writer - by Dorothea Brande