One of many things novelists have to watch out for, when it comes to good ol' show don't tell, is not to drop in a big block of background information in one (or, heaven forbid, several) paragraph(s) of narration. You have to find more artful ways of giving your readers the information they need to follow the story. This is especially tough, as a number of you can attest, when you're writing in an "alternate world" situation like sci fi or fantasy, because there's so much worldbuilding that needs to happen. That's part of what we love about reading stories in those genres: the immersion in a world that's not our own. The staircases at Hogwarts move on their own.
But you as the writer put in a lot of time crafting the details of that world. You probably have a "story bible" that's longer than the manuscript itself, explaining all the nuances of how different the gravity is on the planet where your novel takes place. That's GREAT. As a reader and as an agent, I want you to know all of those things about your work. But what I don't want is for those details to get in the way of the actual story. I don't want the plot to grind to a halt while you detail the etymology of a word you made up. If I really have to know that in order to "get it," you as the author have to find another way to explain it to me.
(Likewise historical fiction: you've done an incredible amount of research to make sure your novel is as historically accurate as possible. It's easy to want to "get credit" for all that time in the library by shoehorning one too many facts into the novel. The story suffers.)
"I know," you're thinking. "I'll put it into dialogue. That way it doesn't count as a big block of exposition, and I've escaped the 'show don't tell' pitfall."
Well, maybe. There are at least two things you have to watch out for, in the exposition-as-dialogue scenario.
First of all, and this is kind of obvious, but based on some of the submissions I get, it's worth mentioning: you can't put quotation marks around a paragraph of exposition and call it dialogue.
Secondly, if you're going to put these details into a dialogue format, it has to actually work as dialogue-- meaning it has to consist of things that one character in the novel would actually say to another. This needs to sound like a real conversation. You can't have Character A feeding all the information to Character B, when Character B's part of the conversation reads like this: "Oh. Mmm hmm. What do you mean? Can you say more about that?"
And now we come to "As you know, Bob." This term refers to a specific subset of dialogue-as-exposition, where both characters already know all the information being explained to the reader. "As you know, Bob," points to a conversation that's really obviously fake: if Bob already knows everything Jane is about to tell him, why would Jane bother explaining it?
Does your manuscript bear signs of "As you know, Bob?" What techniques do you have for ferreting out those moments in your work? Do you have any pointers for providing those crucial world-building details in a more subtle and non-plot-derailing way?