You’ve probably heard before the advice to read your work aloud when you’re editing and revising it. So I’m not here to give you new advice, I’m just here to testify: Do it. Really.
It helps not just for making sure dialogue flows naturally, character voices are distinct, etc., but also with basic stuff like errors of grammar or syntax. We get so used to staring at those words on the page that they become a sort of visual white noise; we know what they’re supposed to say, what we meant to say, and sometimes our eyes just slide over errors because we’re seeing our mental story instead. It’s useful to shift the story into a different form to review it, so your reading brain can’t take shortcuts. (Another method that operates on the same principle, if you can’t or for some reason really don’t want to read aloud: Change the document’s font when you start to revise.)
Last night I read aloud to myself the first half of the story I worked on all weekend, a story I’d been fiddling with in minute and meticulous detail, and it wasn’t until I heard it that I registered I’d used the expression “pretty sure” a half-dozen times in the first couple of pages. It’s a phrase I type so often in my own casual chat and correspondence that my reading brain completely failed to see it until I had to say it.