Most of my advice stems from the premise test.
An <ADJECTIVE> <PROTAGONIST TYPE> must <GOAL> or else <STAKES>. They do this by <DOING> and learns <THEME>.
It seems simple, but it’s actually a powerful and merciless tool that exposes flawed or incomplete thinking. It’s simplicity covers a lot of complexity and theory, so it’s much harder than it looks. I’ve written a lot about premise, the point is to give a clearcut sense of the who/what/where of the story and to express how the idea will be conveyed in an active and interesting way.
Of course, it’s easy to write a weak or incomplete premise test. For instance:
A HOMOPHOBIC MOTHER must MOVE HER DEAD SON’S EFFECTS OUT FROM HIS APARTMENT or else LOSE THE LAST PART OF HIM SHE CAN ACCESS. She does this by MEETING HIS LIVE-IN LOVER and learns TOLERANCE.
That’s not really a premise for a movie, because it’s only described one scene, and not even a scene from the second act. Unless this is going to be a stagey, talky movie about one long conversation in the doorway of an apartment, I have no idea what this script will read like.
That’s why I give this advice. Before you write a screenplay, before you write an outline, before you break out the index cards do this:
Write a fifty word pitch on the scene from the second act that you can’t wait to write. This should be a scene that showcases your talent as writer, is entertaining, and something that fully utilizes the concept you’ve set up.
The mother has a brief affair with a barista at a coffee shop. Not bad, I can envision that, but it has nothing to do with the setup. You could slot that into nearly any drama.
The mother kills the lover with a hacksaw. Okay, that’s gives me an idea of the movie someone wants to write. I’d question the necessity of the setup, but at least it’s an involving intro to a thriller.
Day six of the road trip. The mother and the lover are in Mississippi, checking off another item from the bucket list. They’re mad at each other, and that expresses itself as they bet on competing boxers. This reads as the strongest for me, because it’s both a pitch for a scene, and it gives me a nearly complete idea of the kind of story this will be.
Try this for yourself. If you can’t come up with one dynamite second act idea for your concept, it might not be worth spending 6 months wrestling with it.