Billy Wilder was one of the greatest writer/directors in film history, having co-written and directed such classics as Sunset Boulevard, Some Like it Hot, The Apartment, and Double Indemnity. What screenwriter wouldn't want a little advice from him?

Well, here are some of Wilder's screenwriting tips:

The audience is fickle. Grab 'em by the throat and never let 'em go. Develop a clean line of action for your leading character. Know where you're going. The more subtle and elegant you are in hiding your plot points, the better you are as a writer. If you have a problem with the third act, the real problem is in the first act. A tip from Lubitsch: Let the audience add up two plus two. They'll love you forever. In doing voice-overs, be careful not to describe what the audience already sees. Add to what they're seeing. The event that occurs at the second act curtain triggers the end of the movie. The third act must build, build, build in tempo and action until the last event, and then—that's it. Don't hang around.

From Conversations with Wilder by Cameron Crowe.