The Dreaded Infodump

I had a young writer ask me for advice on how to weave exposition into her fantasy story. The "infodump" is a hurdle for every worldbuilding storyteller. Readers need to know certain things about the world, but they don't want to be bogged down with endless exposition. I figured my answer might be worth posting here ...

The main rule is: Don't ever give the reader information until the reader wants information. Manipulation is your friend here. Tease the reader with the possibility of a answer and then cut that answer short. It helps if your hero is in the exact same position of ignorance as the reader, because then they can become a proxy for the reader's frustration. Make the hero FIGHT for answers so that when she finally gets them, it's a kind of victory. And even when you do explain something, don't explain everything. Tell just enough to keep the story moving forward. Because at the end of the day, that's the exact amount of info that the reader wants (and not a word more). Another trick, always make sure that your "answers" generate even bigger questions ... thus putting the reader back on the hook.
Consider the first Harry Potter book. Re-read those first fifty pages and you see how brilliantly Rowling manipulates readers. The first Hogwarts acceptance letter shows up at the Dursleys, and we're mildly curious what it might be. But then the letter is destroyed before we can read it! As is the next letter, and the next ... It's not until page fifty-five(!) that Hagrid tells us that Harry is a wizard. By the time we read that actual letter, readers are practically drooling.
There's a lot more to say on this subject, but the above is a good place to start!