Once upon a time there was a _____ .
Every day, _____ .
Then one day _____ .
Because of this, _____ .
Because of that [or] However, _____ . (repeat as necessary)
Finally, _____ .
This is important because _____ .
This template derives from a talk by Trey Parker and Matt Stone of South Park and the Pixar story point list (via Brian MacDonald's Invisible Ink as related by Emma Coats) with a few tweaks by yrs trly. While the ideas expressed by Parker, Stone, and MacDonald are not new, they've certainly been distilled to their purest essence. This is an extremely useful tool for finding & strengthening the spine of your main story as well as all the characters' personal sub-plots.
"Once upon a time..." identifies the protagonist/s. This can be an individual, a group, a team, a family, or a community.
"Every day" = the status quo, mundane or outrageous; good, bad, or indifferent. This is the backdrop against which change (i.e., story) will occur.
"Then one day" = permanent change or the potential for permanent change. Whichever it is, it will force the protagonist/s to respond. There is no point in having an inconsequential or self-correcting change (i.e., the status quo returns on its own, including the protagonist/s acceptance of it). Any change that causes the protagonist/s to react is an important change to them even if inconsequential to others. And it can be self-change; the protagonist/s can decide they’ve had their fill of the current situation and will do something about it.
"Because of this" = the step/s the protagonist/s take to either restore the old status quo or establish a new one of their liking. This is what your story is about, even if the protagonist/s later change goals/objectives/tactics as a result of challenges they encounter.
"Because of that" = a direct reaction to the preceding plot point. Whatever "this" is in response to "then one day", "that" will be a further response. It can be either an obstacle or a help (or even a combination thereof) but it changes the nature/direction of the protagonist/s' response.
"However" = an alternative to "because of this", a random and/or external event that adds a new complication/element to the story. Sometimes a "however" is a response to a much earlier plot point that the protagonist/s have moved past but are now forced to deal with again. "Howevers" are permissible to make the protagonist/s' objective more difficult to obtain, they're cheating if used to arbitrarily help the protagonist/s without consequences.
(repeat as needed) = follow the story through logically, with appropriate responses to prior choices or plausible random external input.
"Finally" = the protagonist/s reach a logical conclusion and new status quo they are either willing or forced to accept (viz. a tragic end)
"This is important" = why this story is worth telling. Unless telling a shaggy dog story, the ending must make a crucial difference to the protagonist/s. If they re-establish the old status quo, the reader must understand why this makes a difference to the way they lived before. (In truth, just as one can never enter the same stream twice, one can never return to the way things were before the protagonist/s were aware change was possible; at the very least a return to the original status quo now includes the wisdom to fully appreciate that status quo.)
As noted, this is useful not only for the main plot involving the protagonist/s but also all sub-plots involving the antagonists and supporting characters. Everybody has a story, and while one doesn't have to fill in the details of every character's story to the same degree as the main plot, it never hurts to know what their story is vis a vis the protagonist/s'. Often a group of protagonists will have overlapping motives for participating in a story, some of which may be at odds with one another. They will each certainly have their own unique manner of dealing with the challenges facing them. Too often supporting characters are empty suits designed to trot onstage, do their business, then trot off. By figuring out what their stories are, one opens up the main plot for far greater nuance and detail.
Caveat! This template will not guarantee a good story. What it will do is make it easier to diagnose your plot, to find/clarify/strengthen the spine of your story. You still have to provide interesting characters, interesting situations, and write in an interesting manner.
And that takes practice…