"The cat sat on the mat is not a story. The cat sat on the Dog's mat is a story." - John LeCarre
Most stories have a central conflict. They have the cat and the dog fighting over the mat. But especially in a longer format like a novel or screenplay, sticking to one strand of conflict isn't enough. Halfway through, your readers lose interest because the conflict seems predictable or repetitive.
In that case, you need to zoom out and see what else could be happening.
In the case of our dog and cat, how does their owner respond to the conflict over the mat?
Does she buy an additional mat--over which the dog and cat fight as well?
Does she take away the original mat--so now the dog and cat fight over something else?
OK, that metaphor goes only so far, and I may already have exceeded that distance, but you get the idea: look at the conflict in expanding circles of impact.
Who besides your protagonist and antagonist is affected?
How do they respond?
What knock-on effects does the conflict have?
Who else could get involved?
If one side tries to de-escalate, how could the other side take advantage?
What's the least likely development? How can you make it plausible that such a surprising thing could happen?
If you apply questions like these to your central conflict, you'll have plenty of material to keep your reader or viewer interested.
