It is widely advised that you shouldn’t begin your screenplay with a flashback. Strictly speaking, it’s impossible to have a flashback at the beginning of your story. If it’s the first scene then what’s it flashing back from? On a pedantic level, it would be more accurate to call it a prologue. You may revisit a different part of this prologue later on in the story, thus creating your first flashback.
So ‘don’t begin your screenplay with a flashback’ is misguided advice. Those who instruct that you should NEVER, EVER have a flashback in your screenplay should simply grow up and get a life. Flashbacks are a natural and essential screenwriting device that can strengthen the narrative, build suspense and develop character. They’re fine, they’re cool, they’re fun…but they’re difficult to place.
What really bugs people about the technique is that most writers implement poor flashbacks to explain an indulgent part of the backstory or express a dull piece of exposition. This kind of writing suggests a TV series of its own: “When Flashbacks Go Wrong”. And let’s face it, a lot of flashbacks are of this quality, hence why so many people advise to stay well away from them.
In truth, using flashbacks is a creative and challenging way to keep your story interesting and dramatic but it’s been tarnished by writers and directors who’ve made it an easy avenue for sloppy storytelling.
Basically what it comes down to is this: backstory and exposition bad, drama and revelatory information good. The trick is to make the flashbacks an organic and ONGOING part of the narrative so it doesn’t jar with the advancement of the PRESENT DAY story. A flashback should do one of many things: build the tension, raise the stakes, develop character, reveal crucial information, make the tea (joke)...
In Signs, M Night used (I think) about six flashbacks that revolved around the car crash of Mel Gibson’s wife. The first few were intriguing glimpses, nothing more, and were carefully structured around the ongoing drama of the alien invasion so that the audience wanted to know what was going to happen. The flashbacks ended with the emotional release of the wife’s death (along with her final words that would have a pay-off later) so it helped to develop Mel’s character and reveal crucial information. Some people dislike the wife’s last words and its pay-off but the basic flashback sequence and its place in the story shows a writer/director who’s on top of his craft.
A few years ago, FLASHFORWARDS were all the rage. This sprightly sibling of the flashback would dramatise a key scene out of context to the normal flow of the story and then tease you to stick around to see how the plot reaches that dramatic point. Opening sequences like to do it quite a lot: Mission Impossible 3 does it, Carlito’s Way and A Perfect World too. The latter films reveal the protagonist’s death and then the rest of the film tells you the story of how he died, which is dissatisfying for me. Ideally, flashforwards should be intriguing and full of tension, not clear and absolute.
Also, if you’ve got a terrific flashforward, you’re at a disadvantage as the audience knows what’s going to happen in the story, to a certain degree. What you want to try to do is defy expectation and avoid predictability so that the flashforward is not the END of the film but possibly just one of the main turning points in act two. That way, when the audience reaches that point, they’ll be none the wiser about what’s going to happen for the remaining twenty minutes or so of the film.
What I love about Closer, written by Partick Marber (directed by Mike Nicholls), is that every scene pushes the story forward (it's a terrific script, so lean, incredibly deft), not one scene is wasted. What's particular interesting is that the narrative continually jumps forwards. Weeks. Months. While not strictly a flashforward, the narrative jumps ahead in time at a few crucial moments but you never feel out of synch with the characters and story.
Flashbacks, flashforwards. Some deride them as storytelling tricks, ostentatious bells and whistles to make up for the lack of story. But they’re not. They have a place. They can enrich and enliven a story. But they have to be done right. Remember, backstory and exposition bad, drama and revelatory information good.