Recently I dug up a work in progress that I started a few years ago. I stopped writing it because I thought it was stupid. After finding it again, I realised I was onto something, just approaching it from a disappointing direction. In this work, most of the sentences started with the word "then" and it made the work sound like a laundry list. Likewise, many sentences in the narration were restatements of immediate previous lines. What are some other things writers should look out for to make their work more concise?
Superfluous words I always go back and strip out 99% of the time during the editing process are very, really and actually.
The basic idea is that every single line, every word in every line, should be serving the story you're telling in some way. Vonnegut summarised it as every line should either move the plot forward or reveal character. Lines do other immediate things, like set the tone or paint a picture of a scene, but those should ultimately be serving those two things, which both boil down to the whole point of telling a story. If you can eliminate words or sentences without changing the meaning of the story, basically you should do it, lest you bore your reader with a whole lot of nothing. If doing so would cut all your description, for example, it shows that your descriptions need to be doing more for the actual story other than filling up the page. Ideally, your lines, obviously including the language you use to construct them, should be doing more than one thing wherever possible. So you should think of them in terms of always doing at least one thing. Action can reveal the important traits or interesting details of a character while also establishing a plot point and/or suggesting a thematic metaphor. Dialogue can convey key information while building character through individual voice and/or revealing the nature of the main conflict. Description can set the tone and pacing, establish the setting, spatially orient the reader in a scene, offer imagery that suggests something symbolic about what's going to happen or what it really means, and reflect the character associated with what's being described. These are just some examples, obviously. Redundancy should become immediately apparent to you when you read over what you've written and ask what new idea, new information or new nuance is added by each sentence. (Unless you're writing with some stylistically repetitive phrasing, a la Catch-22, in which case the repeating phrases should be subtly transformed by context and character each time so that you can still say each one adds something different, anyway. This is just one example of how you can kind of break these rules if you're not really breaking them.)