I'd better start with a proviso: I'm not one of those people who thinks films and books are essentially the same thing and therefore require exactly the same set of skills to write. I'm well aware that the two media have different abilities, conventions and limitations. All the same, there are useful lessons that writers can learn from the movies – and here are some of them.
1. Show, don't tell
Yes, I know it's the most basic 'rule' we as writers have. Yes, I know it can sometimes be usefully broken. But if you're struggling with the concept of showing rather than telling, it might be helpful to think about film as a medium. Because 'show, don't tell' is precisely what a film does.
How do we know a character in a film is angry? By how he looks, what he says and what he does. How do we learn what someone's personality is like? By seeing her in a series of situations and getting to know how she reacts. You'll never hear a character who's experiencing a strong emotion yell 'I'm so angry!' or sob 'I'm so unhappy!' And (most of the time) you'll never see a character turn to the camera and tell you who they are, what they like doing and what's their greatest flaw. So if you want to show rather than tell, imagine your character in a movie. If they wouldn't naturally say a particular line out loud in that context, don't write it as part of their POV.
Incidentally, writers can go one better than filmmakers here – because we can describe a character's situations and reactions using all the senses, not just hearing and sight. Get it right, and your scene can be even richer and more immersive than it would be on film.
2. Cut the backstory
A two-hour film leaves no room for lengthy setup or exposition. Most of the time, the audience is thrown into the action and expected to work it out as they go along. This is particularly relevant to sci-fi and fantasy authors, who often feel as though they need to explain everything to their readers up front. In that sense, filmmakers tend to give their audience more credit than writers do. People don't want or need all the details of how a world works before they even get into the first scene. They can figure it out for themselves.
3. What you don't say can convey more than what you do
A good actor can make one speaking glance worth a whole paragraph of dialogue. Likewise, a good writer can say in a single sentence what someone else might have taken a whole paragraph to get across. Guess which one has more impact?
In a way, this is another example of 'give your readers more credit'. People are very good at picking up the subtleties and reading the subtext. And anything has more impact when it's used sparingly than when it's scattered all over the place like confetti.
4. Don't let the special effects drive the narrative
I'm sure we can all think of films that are stuffed full of special effects but have little in the way of plot, realistic characters or emotional heart. There are plenty of ways that this comes up in writing, too. Strings of gratuitous action/sex scenes with little to hold them together, for example. Or details of a fantasy world crammed in for the sake of it rather than because they're relevant to the characters at that moment. Even clever structural devices or a love of flamboyant language can become 'special effects' if they're allowed to take precedence over the story itself. Whether you're dealing with a book or a film, it's the characters' journey that the audience will remember in the end.
5. No-one will notice the deleted scenes
We've probably all been there: agonising for hours about cutting a particular scene from a book. We know it needs to go, for reasons of length or structure or plot. But we're convinced that everyone who reads the book will get to that point and see the gaping hole where the scene used to be.
If you ever find yourself in that situation, just think of a DVD. You've watched the film itself, and now you turn to the extras and start watching the deleted scenes. Did you notice their absence while you were watching the film? Can you even remember where half of them should fit? Probably not – because what you saw was the finished product. You weren't aware that the deleted scenes ever existed, and so you didn't miss them. That's what editing is all about.
That's it from me, but I'm sure there are other lessons that writers can learn from the movies (and indeed vice versa). Please feel free to add them in the comments section!
Write Every Day: tip of the week
Take a scene from your book and imagine it's going to be filmed. Now describe the scene: what happens on camera, what the characters say, details of the setting. Make sure you restrict yourself to only what the audience will experience – in other words, any explanatory or inferential text is out.
When you've finished, read back through the scene. What's it like? Is there anything in it you can use?