Finding the right book at the right time on a topic can be a step from one level of comprehension and ability to the next. These three books are the most transformative photography books I've found. Taken together they will get you from enthusiasm to proficiency. Exactly how proficient is up to you.
The order is important. Skipping ahead will lead to confusion and frustration. Each book stands alone as a complete unit. You don't have to get through all three to learn something. Even just working through the first book, Understanding Exposure, will take you a long way.
Understanding Exposure by Bryan Peterson
This book covers the mechanics of photography in a concise, understandable format with a clear purpose - to understand how to get the right amount of light into the camera and get the correct exposure. With the mechanics out of the way the book delves into some of the "rules" of composition with plenty of examples. Then it wraps things up with a sort of field guide to common scenarios.
You should step away from this book excited that you actually know what the heck is going on when you take a picture. Equally important, you'll have a few tricks like the rule of thirds that will help you start taking better pictures right away. And when things don't go right you'll have a better shot at figuring out why.
Learning to See Creatively by Bryan Peterson
This book is all about the content of a photograph - composition, form and color. Gear is covered, primarily lenses, but only to the extent of understanding how different gear can be used as a tool to get the desired result. The book assumes you know the gear and how it works (that's why you have to read these in order!).
Light, Science and Magic by Fil Hunter, Steven Biver and Paul Fuqua
Roll this book up and smoke it. It will expand your mind! The book is divided into theory and practice. The first three chapters will wrap your head around light as the medium of photography. Once that sinks in it all comes together.
The practice sections are useful when you're ready to digest them over time. You can probably skip the 700 page treatise on photographing metal on the first read.
Remember, reading the books alone is not enough. There are many exercises to try and examples to stare at until they are burned into your brain. Seek out criticism and help from other photographers along the way.
Now go read, try things, get stuck, re-read, try again, repeat.