Trey Parker and Matt Stone are the writers of South Park, a show that should need no introduction (but if it does, it's a hugely popular, long-running animated show on the Comedy Central network). The pair don't often hand out writing advice, but when they do it's worth listening to. One such example is to consider the 'Therefore & But' rule when examining the beats of your plot.
According to Matt and Trey, if you can break down your story into events that are preceded by either the word 'therefore' or 'but', you're on the right track. In contrast, if you ever find an event that can only be preceded by the phrase 'and then this happened', then that's a huge red flag. Your story should never include random events that spontaneously materialise out of thin air merely to move the plot along. This is a hallmark of bad writing and most often occurs when a writer realises that 'x' has to happen in order to progress the story, but there's no earthly way that 'x' would ever happen organically in the story they've developed so far, so they just let it happen anyway...
The following example is the bare bones plot of a South Park Episode called 'Make Love Not Warcraft' where our four protagonists Stan, Kyle, Cartman and Kenny meet misadventure when playing their favourite computer game. Let's see how we can take this episode's storyline and apply the 'Therefore & But' rule.
The boys are playing Warcraft online.
But...
They're killed by another online player, a bully.
Therefore...
The boys gather all their friends online to battle the bully.
But...
The bully still manages to defeat them.
Therefore...
Cartman convinces his three friends that they need to train and become masters of the game.
Therefore...
Each of them develops theirs skills.
Therefore...
They fight the bully once more.
But...
The bully is still too powerful!
But...
Randy (father of Stan) is able to give Stan the 'Sword of a Thousand Truths' (which he acquires through a subplot of the same story)
Therefore...
The bully is finally defeated.
As you can see there's a nice progression of events in this story, each element leading to the next in a logical and believable way. The subplot involving Stan's dad (Randy) also follows the same rules.
Randy asks Stan what World of Warcraft is about and gets told he wouldn't understand.
Therefore...
Randy creates a World of Warcraft character to prove Stan wrong.
But...
Randy is a bad player and gets killed almost straight away.
Therefore...
Randy gives up.
But...
The owners of World of Warcraft (who want to save their game from the bully) give Randy the 'Sword of a Thousand Truths' because they can't find their real champion - Stan.
Therefore...
Randy re-enters the game to give the sword to his son.
Looked at this way the elements of a story are like the runners in a relay race, each handing the plot on to the next in line till the race is run.
Would your story survive this kind of analysis? Try throwing in some 'therefores' and 'buts' and see how it pans out.