From Wally:
One thing I see with new screenwriters is their propensity to tell the story, rather than show me the story. Remember, you are not writing a novel… you’re scripting a story.
If you’ve done your prewrite, you’ve written a treatment, a scriptment, or filled out a beat sheet… in other words you have already written your story. Now you are going to script it. Lay your story out in sequences of scenes that actors will act out, to be seen in theaters or on TV.
In other words, you are creating a blueprint of a story, that a director, with the help of actors and a crew will turn into a movie, or television production.
So, now you know, the story (the treatment or scriptment) is the written story. The screenplay is a script developed from that treatment… what will be seen and heard by an audience.
Wait a minute, you might be shouting! What about movies that are based on a true story, a novel, or a short story? What about them? The screenwriter must still study the story, and decide which parts will stay and which parts must go. Unlike a novel or a historic tale, a screenplay is limited to a set time frame, 90-110 minutes of screen time. Granted, a series gives the screenwriter more wiggle-room, but even series are limited, by episode length and audience acceptance. Your job as a screenplay writer is to write only what will be seen and heard by the audience.
In other words, don’t write “Laura feels sad,” or “Laura looks sad,” write “Laura puts her hands to her eyes, attempting to stop tears.” We can’t see a feeling, but we can see hands move towards eyes to stop tears.