Whether you're writing a 1,000-word essay or a 70,000-word+ book, narrative arc refers to the overall structure of your story. What is presented to the reader first, second, third, next, and so on until the end.
The narrative arc may or may not proceed in chronological order; in fact, chronology/timeline can be and often is entirely separate from narrative arc.
Most memoirs, for example, begin partway through the actual chronology, leading with an inciting event or a key piece of riveting and tension-filled scene.
The less your piece relies on chronological presentation, the more clarity readers need in terms of guideposts, so they understand how to navigate the story and orient themselves within it as they read.
(And the longer your piece is, the more this same suggestion applies. Shorter pieces offer, by definition, a more finite narrative, so the beginning/middle/end is obvious.)
Put yourselves in your readers' shoes: we don't want to struggle to figure out what's going on, or which character is which, or why any of it matters. Writers who plan, arrange, and present a clearly defined narrative arc will always have more success than those who don't.
Narrative arc is the map we writers must follow even though we don't necessarily give our readers specific turn-by-turn directions.
So let's assume we're clear on that piece.
What transitions do we truly need to include in our work that, if we omit them, will cause the reader to be completely lost and give up in frustration?
Far, far fewer than you imagine. And those are the only ones to use.
We can trust our readers to understand that action A happened before action B without using flat transitional phrases like this happened and then this happened.
If a passerby requests directions to the grocery store, you don't need to point out each house they'll pass along the way and who lives in them, or how many pebbles are in the path off to the left where bicycles can cut through, or veer off into an unrelated tangent about an elm tree that used to stand on the west corner but came down in the last tornado and is now just a sad stumpy thing. Where does our passerby need to go? The grocery store. That's the end goal.
Similarly, if you find you need to provide an overload of transitions, the likely issue is that you haven't gotten clear yet on the true narrative arc, inclusive of that end goal.
Map out your story chronologically—the time bound place in which we all live in the world—then rearrange the pieces/chapters with an eye toward presenting a narrative arrangement that gives readers the best, clearest story.
When do they need to understand who the characters are, and how do we introduce them? What even is our story and why does it matter? Is the bully on the elementary school playground a necessary part of the story or a distracting detail?
