Margins should be at least 1.25 inches on the left and at least 1 inch on top, bottom and right. Smaller margins will look you're "cheating" to fit more on the page. 7) Your dialogue blocks and the character name above them should be tabbed in, not centered. The dialogue block should be 3 - 3.5 inches wide.

The movie producer and all-around mensch Stuart Cornfeld once told me that in a good screenplay, every structural unit needs to do two things: (1) be entertaining in its own right and (2) advance the story in a non-trivial way. We will henceforth refer to this as “the Cornfeld Principle.”