Ernest Lehman's 4 credos of a good movie

Ernest Lehman is famous for writing movies made by Hitchcock (North by Northwest and others), Mike Nichols (Who's afraid of Virginia Woolf), Robert Wise, and many other greats. About movie screenplay structure, he said:

In the first act, it's who are the people and what is the situation of this whole story. The second act is the progression of that situation to a high point of conflict and great problems. And the third act is how the conflicts and problems are resolved.

In 1997, the WGA interviewed Lehman for their "The Writer Speaks" series (youtube link). On a more granular level, these are the credos for a good movie screenplay that he mentioned:

• It is a succession of scenes each with a definite conflict.
• The dialogue is as clever as can be without seeming clever.
• Exposition is always concealed.
• Never confuse an audience for even 5 seconds.

For more on Ernest Lehman, read the excellent book "Ernest Lehman: The Sweet Smell of Success" by Jon Krampner.