Once upon a time I had a writing teacher tell me "Show, don't tell". I know now this is incomplete advice at best. A better way to put it would be, "Show what needs to be shown, tell what needs to be told."
That leads us to a new problem: how to know when to do either of those things. And, again, that led me to come up with a further refinement on the slogan: "Show the things that are best dramatized; tell the things that are best spelled out."
This process is an art, not a science (like all writing is), and so sometimes the only way to figure it out in a given work is to feel your way through it.
We all know about the "info-dump", that bane of bad SF. (Well, I should say alleged bane, because I see oodles of published SF bristling with page-long infodumps. I sometimes think many of the prescriptive prohibitions in this vein were not cooked up to improve the state of the art, but as gatekeeping shibboleths: write a few stories where you don't infodump to prove you can do it, and then once you're in the club, you can dump all you like because who's gonna stop you? "The trouble with publishing is that you go from not being published no matter how good you are, to being published no matter how bad you are," as Tibor Fischer put it.)
Cough. Okay, rant over. The problem is not that we should not convey some information directly to the reader, but that we should not do it at protracted length, or artlessly. A dump is okay as long as it doesn't sound like a dump, but rather some vital part of the story. Flight Of The Vajra has some dumps in it, but I tried to keep them funny and pointed, by having the protagonist deliver them in his acerbic voice.
Sometimes, though, you just need to tell people stuff and get it out of the way. The opening of Blade Runner has a short textual crawl that tells us the most important things we need to know about our setting, the better to plunge us directly into the atmosphere and action of the story. But the narration that plagued the earlier editions of the film was expunged; everything we learned from the voice-overs, we could glean from the moody imagery and the soundtrack anyway.
I had to do a little juggling in this vein with my current work-in-progress, Unmortal. Whenever I had to explain something because of its functionality or behavior, I tried to slip that in around the parts of the narrative where it made sense. And — I think this was the real key — I tried to get all the heavy, showstopping explanation out of the way by the time the first fifth or so of the book was up, so from then on I could concentrate on the actual story. I also used another trick I'm fond of, where I have people talk about the goings-on in the world by embodying opposing sides of it, or debating its merits. That way instead of those things being "As You Know" abstractions, they're a little more alive.
For all I know, I probably got it more wrong than right at this stage. But I still have a few more passes on the story before it's anything like exhibitable. If by then I get it more right than wrong, I'll be happy.