When writing fiction, especially in universes other than our own such as sci-fi/fantasy genres, the reader often has to be given a piece of information about how the world works in order for what's coming up to make sense. However, this piece of information should be common knowledge to the characters in the story.
In narrative voice, such as writing a novel in storytelling style, it's often sufficient to simply drop in a footnote paragraph, allowing the narrator to explain as if the reader were standing next to the narrator watching the scene unfold. It functions, if you can keep it short to avoid taking the audience too far away from the plot; if you need two pages, inlining it into a conversation between your characters probably isn't the way. However, in screenwriting, you often don't have the luxury of this device; one of the characters simply has to say it. There really are only two main ways I know of to give the information:
The idiot/noob/relief character asking the audience question. This is a convenient way to exposit facts that may not be completely common knowledge to everyone in the universe, however a character that isn't completely in the know isn't always available in a plausible way. This is probably the primary workaround to the title trope when a narrator isn't available in the storytelling format, and it's probably more common now in part because it can be subtly done without "cue words" that clue in the audience to the use of a common device.
"As you know...". This is basically lampshade-hanging; the characters know that each other should know what they're about to say, but they're going to say it anyway as a lemma to make their next points (and to get the reader up to speed). This is, IMHO, overused to a fault, and few screenwriters can get away with playing this trope straight anymore; they have to either "deconstruct" the lampshade, making an even bigger deal about the fact that they shouldn't have to say what they're saying, or else they play with it, either putting the line at the end of the exposition as an admonishment ("You should have known that"), or having the character being exposited to say "Yeah, I know, but..."
The only other way I can think of to give the user the information is, well, not to give it. Have the characters act the way they would in an everyday situation where everyone knows the thing the audience doesn't, and the audience just has to come along for the ride and pick up the fact by context.
Conceptually speaking, besides these devices, how do you give your audience information that they shouldn't have to ask for if they lived in the world of the story?