The best button is already in the scene, one beat before you stopped.

A button is the last beat of a scene, the line or the image that makes the cut feel decided instead of accidental. Most scenes in a first draft don't have one. They stop when the information runs out, and the reader feels the page end before the scene does.

Watch Miranda Priestly in The Devil Wears Prada. Aline Brosh McKenna gives her two words and uses them over and over. That's all. It ends the scene and it tells you who owns the room at the same time. The button isn't decoration. It's one character putting a period on somebody else's sentence.

A button does one of three jobs. It lands the turn, so the last line is the thing that changed. It reverses, so the audience walks out of the scene thinking the opposite of what they thought walking in. Or it hands off, so the last image is the question the next scene answers. Chinatown ends on a handoff that's also a verdict. Robert Towne gives the whole movie to one line about a place, and then there is nothing left to say.

Try this on your own pages. Read the last four lines of any scene out loud and cut upward until the scene ends on the strongest one. Usually two or three lines are sitting past the real ending, written because you were still thinking. Those come out.

A script with buttons reads fast, and a fast read is what counts when you're fourth in somebody's weekend pile. Nobody finishes a script out of fairness. They finish it because it kept ending scenes before they could put it down.