Dan Wells has an excellent set of YouTube videos on story structure, made at a conference in 2010. I don't necessarily remember information very well from videos, though, so I decided to take notes and publish them here. Since he got the idea from a roleplaying game book, and I'm giving full credit to him, I assume he won't mind.
The first video is here:
There's also an episode of the Writing Excuses podcast that Dan does with Brandon Sanderson, Mary Robinette Kowal and Howard Tayler in which he explains the seven-point structure. I haven't re-listened to that to add to my notes; they're solely taken from the videos.
Whether you are an "outline" writer and do the seven points upfront and then write the story, or a "discovery" writer who writes first and then incorporates the seven points during revision, the system is still useful.
Start at the end, with the resolution - the final state of the characters/plot - and move back to the hook, then the midpoint, the two plot turns in order, then the two pinches in order.
Here are the seven points.
In the hook, the character is in the opposite state from the state they will be in eventually. For example, if they are going to end up strong, start them out weak.
(Harry Potter lives in a cupboard under the stairs.)
2. Plot Turn 1
Something changes that puts things into motion. New ideas, new people, a Call to Adventure or inciting incident, starts the movement from the situation of the Hook to the situation of the Resolution.
(Harry Potter learns he's a wizard, enters the wizarding world.)
3. Pinch 1
Something goes wrong that forces the character to step up and solve a problem.
(Harry Potter and friends fight the troll.)
This is the point at which the character moves from reaction to action, decides to move towards the end state (knowingly or otherwise). It doesn't need to be in the middle of the story. In a mystery story, for example, where the midpoint is deciding to take the case, it can come very early on.
(Harry Potter decides that people who suck blood from unicorns must be opposed.)
5. Pinch 2
Something goes very wrong, much more so than in Pinch 1. These are the jaws of defeat from which victory must be grasped. Mentors die or vanish, allies prove unreliable, plans fail.
(Ron and Hermione fall to the magical traps on the way to the Stone and leave Harry Potter to go on alone.)
6. Plot Turn 2
The character receives the last piece needed to create the resolution. "The power is in you!" is a classic Plot Turn 2. Grasping victory from the jaws of defeat.
(Harry Potter looks in the Mirror of Erised, and because his motives are pure the stone goes into his pocket and he knows that if Voldemort touches him it will harm Voldemort, not him.)
This the climax, what you're leading up to, what the story's about.
This can be plot or character. For example, the character makes a moral decision and becomes a different person from the person they were when they started. The problem of the plot is resolved.
This can be a state rather than an action (example of Poe's "The Telltale Heart", where the resolution is that the narrator is insane).
(Harry Potter defeats Voldemort.)
A tragedy plot reverses the order of "all is well" and "all is terrible". The former is the hook, the latter the resolution.
This is the bare skeleton. Round characters, rich environments, try-fail cycles, subplots flesh it out.
The Ice Monster Prologue
The name of this is taken from Game of Thrones. Because the magic and action don't appear for a long time in the book, there's a prologue to introduce the promise that they will eventually arrive. (The hook itself isn't necessarily exciting, because it's the opposite of the final powerful state of the character.)
Before heroes succeed at anything important, they should earn their victory by trying and failing multiple times. A problem that can be solved first go isn't big enough to be interesting.
A try-fail can show the consequences of failure (Indiana Jones, the guy who drinks from the wrong chalice). It can look like a victory (Princess Bride, where defeating the swordsman, the giant and the Sicilian brings the Man in Black closer to his goal but he doesn't reach it yet.) It can be an actual failure (Inigo Montoya trying to avenge his father.)
Plots and Subplots
Plots, subplots and character arcs can each be mapped out with the Seven-Point System. Spread out the events to create good pacing; line them up (have more than one advancing in the same scene) to create powerful moments, e.g. the resolution of one is the pinch of another. Character and action resolutions can come in the same powerful scene.
I hope that's as useful to you as it will be to me. Thanks to Dan Wells for laying it all out.