People will advise you to write all sorts of sentences. Snappy sentences, lyrical sentences, Hemingway-esque short sentences, long Faulknerian sentences. But there's really only one kind of sentence that actually works: a sentence that carries the reader forward from the previous sentence. This is harder than it sounds.
I don't care what kind of fiction you're writing. Introspective or action-packed, sprawling or tightly focused, character-driven or idea-driven — it doesn't matter. You can write any kind of story you want, and this still applies. Each of your sentences has to build on the previous one, propelling the reader forward.
Usually, I'm a big fan of saying there are no rules in fiction-writing, just suggestions and lists of things that are hard to pull off. But I've been thinking about this one a lot lately, and it feels pretty iron-clad: Your sentences should build on each other.
Part of the joy of reading, especially fiction, is the feeling of being swept forward by narrative, and following the chain of statements from A to B to C. We read to "find out what happens next," but also just to follow the thread.
At this point, a lot of people are probably slapping their foreheads at the obviousness of what I'm saying here. Of course sentences should follow each other in some kind of narrative or logical progression. What else would they do?
But I feel like this is easier said than done, and I read a lot of fiction that fails to do this. You know that thing where you're reading a book, and your eyes just slide off the page and you find yourself not reading further? It's like you just can't read any further, even if you want to?
Yeah, that's probably due to sentences not building on each other.
I encounter this problem a lot in fiction, and I've noticed it in some stuff I've read lately. It can happen with well-written, beautiful sentences, or with clunky, stumbly sentences. And it's one of the easiest problems to miss, when you're revising your own work — because you either look at each sentence individually, to make sure it's a good sentence on its own, or you skim the whole section. Plus you know where this is going, because you're the author.
This is especially a big issue in science fiction and fantasy, because immersiveness is such a huge part of world-building. And your readers can't get immersed if you don't carry them from sentence to sentence.
It's about Narrative Flow.
The more books I read and the more stuff I try to write, the more I'm convinced that story is everything. Telling a good story, in a way that engages people, is the best thing you can do, no matter what kind of story and how you tell it — and a huge, ineffable part of storytelling is momentum. Readers (or audiences) need to feel like they're being carried along on a current of story.
Words might be the atoms of storytelling, but sentences are the molecules. Verb by verb, they propel.
Often the best works are the ones which feel like they're sort of taking you by the hand — but this doesn't have to be literal hand-holding. In fact, some of the most difficult, impenetrable works of fiction are the ones which do the best job of having sentence lead to sentence — even if they're challenging you along the way. Samuel Richardson's Clarissa and David Foster Wallace's Infinite Jest are both 1,000-plus-page tomes, which challenge contemporary reading sensibilities in different ways — but they're both ferociously propulsive on a sentence level.
Here's an example of a reasonably well written paragraph where the sentences don't really seem to follow on from each other:
The Captain was in another one of his stygian moods, as if sensing that mutiny was a subject of conversation below decks, in the radiation-drenched catwalks close to the engine core. Babies have an innate awareness of motion, but they can't distinguish shapes very well, and it's part of why they don't know other people as separate individuals. The spaceship was swan-shaped, but Nestor often thought it was more like a big ugly goose, that honked and shat at the same time. Anti-matter is not stuff you want to be juggling when you're drunk.
Okay, so that's sort of an extreme example — those sentences are all literally non-sequiturs — because this is often a subtle problem and it's hard to dramatize. The point is, just reading the above four sentences is exhausting, because there's no thread carrying you from one to the next. After the sentence about the captain's bad mood, you want the next sentence to tell you more about either the mood, or the mutiny. Maybe a description of the captain's grumpy mannerisms, or the noises on the catwalks.
I feel like I see a less extreme version of the above example pretty often — sentences that are perfectly okay in their own right, but don't build on each other, or create any sense of momentum.
Types of non-building sentences
At least in my own writing, I see this happening a few different ways:
1) The gorgeous sentence that gums up the works.
Sometimes you write a sentence that you really, really like. Even though it doesn't actually add anything to the surrounding sentences, or make any sense with the flow of the other stuff going on in this section. It's just such a nice sentence that it's hard to let go of it. But sometimes you find that one particularly beautiful sentence messes up your whole flow, and you have to sacrifice it for the good of the herd.
2) Saying the same thing over and over.
Sometimes, you write three sentences in a row that basically just say the same thing in slightly different ways. Put another way, you sometimes have sentences that just restate the same or piece of information, with only minor variation. Or think about it this way: sometimes, you fail to notice that you've written three sentence, which only dispense a single nugget of description, action or emotion.
3) Straight-up non-sequiturs.
Like the example above. Except that of course you could do that on purpose, as a stylistic thing, and I could see making it work. It's more just that if you don't intend to have all your sentences skipping from topic to topic, with no apparent order, you may have a problem.
4) Just a general lack of focus.
This is the most common problem, and the hardest to diagnose. Maybe the sentences are all following a topic, and they're progressing to a large extent. But at the same time, things are just... gumming up. And part of this gummage is the fact that there's no strong viewpoint or narrative voice in this section. Each sentence just feels slightly disconnected, or like it belongs in a different paragraph than the others.
How to diagnose this problem
The most obvious thing is just to re-read your work 1000 times, until things jump out at you, or claw at your subconscious while you're in the bath. But once again, there's the problem where you skate over some of the flaws in your own work because you know how it's supposed to flow and you can't really see past that.
But hopefully you're getting feedback from other people on your work — either beta readers, or a writing group, or just random people on the subway. And you can often spot warning signs, when people say things like "This is where I started to bog down," or "This part felt really slow to me," or "This is where I wanted to skim." Often what the reader perceives as "slowness" isn't that nothing is happening — it's that the sentences are not carrying the reader ahead.
But also, this is one reason why reading your work aloud is so important. There is no substitute to reading your own work aloud, either alone or to an audience. You can pretty much instantly tell if the sentences are not flowing right, because it'll be hard to read aloud. You'll find yourself stumbling or pausing more, because the sentences aren't smoothly leading into each other.
The bottom line is that your prose doesn't have to be breathless, or dynamic, or action-packed, or even particularly easy to read. But a lot of what makes a strong narrative comes down to the flow, from sentence to sentence, and if people are feeling as though there's too much static in your signal, take a hard look at how your sentences are following each other.
Often, the best sentence isn't the most clever or the most beautiful, but the sentence that picks up right where the previous sentence left off and moves the reader along.