Backstory that doesn’t exist

As I noted a couple of days ago, it’s difficult to recap a complicated backstory. It can also difficult to recap a backstory that doesn’t exist.
Which is, of course, the challenge most of us writers have: At the start of the book, everyone has some sort of history, and if it’s important, we have to let the readers know about it, as efficiently as possible. In fantasy or SF, it can be even tougher because we’ve got a whole world’s backstory, and possibly different laws of reality to explain.
So how do we do it?
•”A long time ago in a galaxy far far away …” A concise history at the start of the story can work, if it doesn’t take too long. And if the material is interesting (assume I append that to every example). Though for me personally, it’s always worked better in films (a lot of historical movies used to do it too) than books.
•Dribs and drabs. Whenever it’s necessary to clarify something, there’s a little authorial mention or a thought balloon (so to speak). If it gets all the information out, this probably works best——minimal intrusion, least chance for the reader to get bored.
•First-person monologue. Having someone spend a couple of pages telling who they are and how they came to be should be just another info-dump, but it always works better for me; the awful Four Fingers of Death, which I’ll get to in my next books post, would have been an even bigger mess if it hadn’t been in a first-person voice. Third-person viewpoint interior thoughts work with this too.
•Conversation. If we can work it into casual conversation——without any sense of a lecture of “as you know, Jim …”——that can work really well. For an interesting exercise, read Fritz Leiber’s Conjure Wife, which opens with a long internal monologue filling us in on a lot of background, and the film version Burn Witch Burn, which presents the same information in a series of conversations. Both work.
•Lecture. Even if it’s legitimate——your character doesn’t know whatever they’re about to hear——it should be brief. If it’s brief and a conversation, so much the better.
One of the things that led me to give up on Cassandra Clare’s City of Bones, which I read last weekend was that while it had many things I liked (good villain, decent characters, competent plot), the teenage protagonist spends a lot of the first half of the book sitting while people explain things. It paces it much better than American Goth did, and the characters talking are interesting, but it still felt like the story stopped dead.
It does make me think about one of my worries for Brain From Outer Space, that characters spend too much time discussing, debating and interrogating instead of acting. Am I worrying too much? Or is it that what looks like a familiar bit of world-buidling to me in City of Bones is a lot more novel and intriguing to the intended Y/A audience (I have been reading this stuff for 40+ years)? I guess I’ll find out when it’s done (finally) and I send it out.