I'm facing starting another campaign, so the usual question has come up:
"What's my plot going to look like?"
...
Any suggestions?
Blimey, that's a big question!
I want something more complex than what they teach in middle school: every story has a beginning, climax, and denouement. I'm tempted to use the three-act structure, which I know like this:
Act 1: Protagonist/audience meets all characters and general conflict.
Act 2: General conflict becomes more complicated, and protagonist gets all-but-defeated.
Act 3: Protagonist solves conflict, against all odds.
In fairness, that three-act structure isn't far removed from your middle-school version - the beginning is Act 1, the climax happens at the end of Act 2/start of Act 3, and the denouement is the scene tacked on after the last commercial break where the stars all go for shawarma or whatever.

There's also a reason that that structure gets used over and over again by Hollywood - it works very, very well.
If I recall correctly, there's also an older five-act structure. We don't see it very often these days, but it was used in "Babylon 5":
Act One: Introductions. (We are introduced to the station, the characters, and their inter-relations.)
Act Two: Rising action. (We meet the Shadows, learn the secret of the Vorlons. Note that this act actually ends mid-way through season three, just before they break away from Earth.)
Act Three: Climax. (The Shadow War and the redemption of Earth is completed. Note that this act actually ends at the end of season four.)
Act Four: Falling action. (The telepath crisis and the Centauri War in season five)
Act Five: Denouement. (The final four episodes, where we see the surviving characters say their goodbyes and leave the station in the hands of their successors.)
However, "Babylon 5" itself shows the big weakness of this structure, especially in the fifth season that just doesn't live up to the excitement of the previous two. That's why most Hollywood movies have a very short "falling action" (where the movie villain comes back for one last, surprise attack!) and "denouement" - you have to have them to wrap up the story, but the audience is already reaching for their coats so make it quick.
For an RPG campaign, the structure I've found most useful is the one from "Buffy: the Vampire Slayer" (or, really, pretty much any Joss Whedon show) - you have a number of episodes, each with their own beginning/middle/end, but also a season-long arc (generally coupled with a "big bad") that
also has a beginning/middle/end. Which, coincidentally, matches the RPG campaign where each session is an 'episode' while the campaign as a whole is the 'season'.
(I also found a lot of the advice in the "Vampire: the Masquerade" books
extremely useful. It's a bit pretentious at times, but it genuinely does a good job of breaking down storytelling into acts, scenes, and 'chronicles', and also touches on things like theme, mood, and so forth.)