Fantasy Q&A: World-Building and Fourth Wall

On a thread at the Fantasy Nano forum, someone brought up a question that every fantasy writer must address.  How do you explain the world-building or "rules" of your world in your novel to the reader without making it seem like you are explaining the world-building or "rules" to the reader.  Because in most fiction, you don't pierce or break the fourth wall--you, the author, don't talk directly to the readers.  It is a convention readers expect to be upheld.

So, how do you relay necessary information to your readers, so they can understand?

There are a lot of tricks out there.  Such as having a character who does not know the conventions of the society.  Or you can let the reader learn by immersion, like how Antonio Banderas's character in The 13th Warrior movie does to learn the language of his host people.  These and sundry other methods have advantages and disadvantages.

But whether or not you have a character introduced the rules of the world like us readers are, it doesn't change the fact that world-building affects more than a single situation.  It affects the whole novel.  This is true in the same way your character will change what plot options and events are possible, because he will only act and react in certain ways, different than another character will.  So, immerse your novel in world-building.  If you want to reveal how a certain magic works, do the obvious scene with it--and then go beyond it.  What indirect effects does this magic type have in the world.

For example, say your character needs to eat a certain plant to do perform a certain spell.  Then think that plant's implications.    

How is that plant integrated into his world--is it illegal?  Is it as common as aspirin?  Do you have to have a script to get it?  How expensive is it?  Can anyone use it?  Who sells it?  

What are the effects of the plant on the body--does it make the user high?  Does it give him indigestion?  Must he use more and more to get the same spell effect?  Is it addictive?  Does it react badly with other plant-based spells?  Does it eventually build up in the body, and the build up kills?

And so on.  Each answer gives you a possibility of showing something about your world-building in the novel.  In a line, in a paragraph, in a fragment of a scene; in a scene, in a chapter.  Small or large.  You can pick which tidbits are relevant to the current scene and show the rest later or not at all.  Some can be implied by the other answers.  You just have to play with it.  You just have to focus your scenes and chapters through an additional lens of world-building, by asking yourself constantly how world-building affects and is affected by this and this and this in your novel.

Basically, world-build in the details of your novel whenever possible.  Let your world-building be inseparable from your rest of your novel and its components of character and plot and so on.