I don't think you necessarily need to read regular books to be a good screenwriter, but it can really help. Reading a good book can make you think about what works, what moves you along, what gets you to read 100,000 words instead of 100 sparse pages.

And once again, good writing just seeps into you and your writing. As a script reader, I often saw writers with good ideas who couldn't find a good sentence with four friends, a talking great dane, and the Harlem Globetrotters.

But since a lot of film people don't have the patience for books, I highly recommend reading plays. Every now and then, take the time you would take to read a screenplay and check out some Pinter, Mamet, Chekhov. See how Neil Simon moves a story along with jokes or how well the speeches from Ivanov hold up.

I shall quote Stephen King: "Never trust a writer who has written more than he has read".

How do you expand your literary knowledge? You need to immerse yourself in all kinds of text-based materials. I cut out magazine articles, organize them in binders if it has story potential. I buy tons of books on different subjects, fiction and non-fiction. I don't think reading screenplays is enough, you need to read books to gain knowledge and expand your vocabulary. You are a writer, you need to force yourself to read. Start with your fave genres and never limit yourself.
So, watch movies, read screenplays, read novels. Repeat.

I'm not much of a novel reader... just movies, screenplays, and writing for me. I have started to read novels just from urge to accumulate more knowledge of the writing world. I've definitely blended how I critically read/analyze novels and screenplays.

Because great writing is great writing in any form.

Reading literature is a terrific way to improve your screenwriting, not just because of the way good literature naturally improves your own sense of language, but since fictional literature is full of bold, inventive storytelling, crammed full of ideas that film hasn't even come close to serving up. By reading literature, your own imagination gets a serious boost, the likes of which just watching films won't provide.

@ Dharmesh -- Haha, I was gonna quote Stephen King as to why it's not as important to be well read. But I think you win :p

In ON WRITING he talks about using your own toolbox. Using what's available to you. Basically, he is saying write the stories you can write, not the stories that are like someone else.

While I truly believe in this standpoint, I also can't argue that reading expands your toolbox.

Also Kurt Cobain talked about something similar.

He mentioned that he stopped playing covers at a very early age (which isn't really true if you look at his discography -- Nirvana Unplugged is almost ALL covers lol).

He said he was learning how to play from covers, but the problem was he wasn't creating anything new. His music was starting to sound like those that he was doing covers of.

He felt it was more important to figure out what you can bring to the medium that is fresh and new, rather than what others have done before you.

In addition to being the consummate film geek, Tarantino also seems to be a voracious reader, with Elmore Leonard being a major influence. This is what he told Creative Screenwriting about Leonard:

"When I was a kid and I first started reading his novels I got really caught up in his characters and the way they talked. As I started reading more and more of his novels it kind of gave me permission to go my way with characters talking around things as opposed to talking about them. He showed me that characters can go off on tangents and those tangents are just as valid as anything else. Like the way real people talk. Actually, in TRUE ROMANCE I was trying to do my version of an Elmore Leonard novel in script form."

I definitely second what Ryan has said above. Reading books, at least in my experience, does improve your writing, as many a writer will advocate. Books do indeed hold narrative strategies that are rarely if ever explored on screenplays. In fact to expand on what Paul said all of your readers should read David Bordwell's article http://www.davidbordwell.net/blog/2009/09/12/50-days-of-summer-movies-part-2/. It shows how Tarantino's narrative strategy borrows heavily from crime fiction and other popular literature. Bordwell has made a point of showing the similarities between novels and films in his writings and I think it is an important observation.
We as screenwriters often forget because of our obsession with screenwriting conventions that we are first and foremost storytellers. Any smart storyteller would be remiss to reinvent the wheel if they didn't have to. Each mediums has its strengths and we can learn from all of them.
If anyone wants to work on dialogue and character, the closest medium in terms of human performance is theater. Why deny yourself the opportunity to learn in any of these arenas. A writer is a writer is a writer.
If you have followed this blog long enough you realize that some of the most successful screen and TV writers also write in other mediums. David Simon(novelist, journalist), Aaron Sorkin (playwright, TV writer), Derek Haas (novelist). I don't believe this is coincidence.