If you’re looking for a comprehensive guide to screenwriting, the first book I’d recommend would be Robert McKee’s “Story: Substance, Structure, Style, and the Principles of Screenwriting.” Quite simply, I believe it’s the “bible” for screenwriting.
To me, no one better understands how all the elements of a screenplay fit together, and no one is better qualified to explain the magic of story construction and the relationship between structure and character than Robert McKee. He has a masterful understanding of the fundamentals of story itself, and he writes with clarity about the basic story tools every writer must develop in order to move beyond cliche and into something original.
Using examples from famous films, McKee educates the reader as to why some stories grip us, while others leave us yawning within the first few minutes. Although it’s written with the screenwriter in mind, this book contains excellent specific and practical guidance on how to craft compelling stories that would be of value to anyone who works in the narrative arts.
The book is a journey through human history and the way we've built stories - as well as a guide that teaches the clues and the structures necessary to write an incredible story. McKee completely dissects what makes a screenplay great while also laying out a roadmap of how to create a solid script.
McKee teaches these same concepts in storytelling seminars, which many industry luminaries have attended. Save yourself several hundred dollars, and buy a copy of his book instead. It’s dense and carries a lot of information, but it's a worthwhile investment of both time and money. I highly recommend this book to everyone interested in the art of writing and the art of telling stories.