William Goldman is a novelist who became a successful screenwriter in the 1960s. His best-known screenplays include Harper (the Paul Newman detective movie), Butch Cassidy and the Sundance Kid, Marathon Man, All the President’s Men,  A Bridge Too Far and The Princess Bride. He wrote this book in 1982, partly as a memoir and partly as a guide to screenwriting. It’s a bit dated now, but it’s still a wonderful book for anyone who’s interested in how movies get made (and how many movies don’t). 

Goldman lists two key lessons for the novice screenwriter (the Roman numerals and capital letters are his):

I. NOBODY KNOWS ANYTHING (i.e. nobody in the movie business knows for sure what will work and what won’t)

II. SCREENWRITING IS STRUCTURE (i.e. there’s more to screenwriting than telling your story in the right sequence, but you’ll never write a good one if you don’t get the story’s structure right).

The biggest lesson I took away from the book, however, is that screenwriting is extremely frustrating. You can make a whole lot of money at it, if you’re very talented and/or very lucky, but you’ll spend most of your time writing scripts that never get made into movies, and when one of your scripts does get filmed, you won’t have any control over what the director, producers, actors, et al. do with it. Film making is a collaborative medium, but the screenwriter is rarely invited to collaborate after filming starts. It’s unlikely you’ll even be invited to a sneak preview.