Some things I've picked up about screenplay structure, mostly from reading scripts and paying attention to the ones that don't follow the rules they're supposed to follow.
The three act structure in a screenplay isn't really three acts. It's two turning points. Everything people argue about when they argue about structure comes down to what happens at those two hinges and whether the writer earned them. The acts themselves are just the space between.
Billy Wilder kept a sign above his desk that read "How would Lubitsch do it?" He co-wrote with I.A.L. Diamond for decades, and their scripts read like they were assembled by a watchmaker. Every scene in The Apartment does at least two things at once. Wilder said, "If you have a problem with the third act, the real problem is in the first act." I think about that constantly. It means structure isn't sequential. It's recursive. Your ending is already broken if your setup is wrong, and no amount of clever plotting in the middle will save it.
Most screenwriting advice tells you that the inciting incident should land around page 12. This is useful the way a recipe is useful. It gives you a starting point. But I've read plenty of great scripts where the inciting incident shows up on page 3 and plenty where it doesn't arrive until page 25, and the difference isn't timing. It's whether the audience has a reason to care by the time it hits.
Phoebe Waller-Bridge built Fleabag from a one-woman Edinburgh Fringe show into a television series, and the structure looks messy if you're scanning for conventional beats. She breaks the fourth wall constantly. She lets scenes trail off. But underneath all of it, the architecture is precise. Every time Fleabag looks at the camera, she's doing something structural: she's telling you what she wants you to believe, which is almost never what's actually happening. The fourth wall break is a misdirection device disguised as intimacy.
A scene that doesn't turn isn't a scene. It's a pause. I didn't understand this for a long time. I thought scenes could just establish mood or deliver information. They can, technically. But if nothing changes between the first line and the last line, you've written a description, not a dramatic unit.
The midpoint matters more than anyone taught me. In most three act structure breakdowns, the midpoint barely gets mentioned. But look at any screenplay that holds your attention all the way through and you'll find something happens around page 55 or 60 that reframes everything. In Some Like It Hot, the midpoint isn't a plot twist. It's an emotional one. The disguise stops being a gag and starts becoming a trap. The stakes shift from comedy to something that actually hurts.
Quentin Tarantino writes dialogue scenes that run seven, eight, ten minutes long because he understands something most screenwriters don't: tension can build through conversation alone. The opening of Inglourious Basterds is a man asking questions at a kitchen table. Nothing happens for nearly twenty minutes. Everything happens. The structure of that scene is a slow tightening, and when it finally snaps, you realize the entire sequence was one long fuse.
I'm not sure whether screenplay structure is something you learn or something you absorb. The writers I admire most can't always explain why they put a scene where they put it. They just know it goes there the way you know when a sentence sounds right. Maybe structure is less a framework and more a sense of rhythm that develops over time, from reading and watching and failing enough that your instincts get calibrated without you noticing.