Michael Arndt won an original screenplay Oscar in 2007 for “Little Miss Sunshine” and now finds himself nominated again, for best adapted screenplay for “Toy Story 3.” But, as he said on Tuesday morning, writing remains a mysterious, difficult process. One of the few things that works for him: He starts by writing the end of the story and figuring out how he wants the audience to feel.He starts by writing the end of the story. Knowing the end of your story is perhaps the most important key to prep-writing and breaking a story.
Yes, it's all well and good to have this romanticized image of a writer, plunking down in front of a typewriter, inserting a blank piece of paper, typing FADE IN and off they go to God knows where, but they just know they'll find their way (this is precisely how the last episode of "Californication" ended, by the way). That may work for you...
But if you're serious about being a professional screenwriter or TV writer, that approach simply doesn't fly. I've never met a writer with any sort of career in Hollywood who doesn't break their story in prep.
And the most symbolic proof of that instinct is what Arndt suggests: Know the ending of your story first