Say you've got this gorgeous world - you've slaved over it, crafted its tiniest details with care, placed characters in it, and now you're ready to tell a story about it. How do you get the world to appear in the background without overwhelming the story?
Let's start with geography.
Some authors can get away with having a page or more of scenery or setting description, while for others it can seem like needless information. Well, if your characters should happen to be on a quest (for example!), traveling through this scenery, then that gives you some opportunities to describe it, but those descriptions can stick out, or be set into the foreground, as digressions.
On the other hand, if the scenery is active in the plot and the inner lives of the characters, it will suddenly be extremely relevant. This can be done with plot events, like in Tolkien's The Hobbit when a thunderstorm leads the characters to take cover in a cave, and they end up getting kidnapped by goblins.
Or when a character-internal deeper point of view is involved, that person's observations of a scene can be colored by, and demonstrate, the emotional state that is about to drive him or her onto the next section of the plot. I'm reminded of agent Donald Maass at the Surrey International Writers' Conference, talking about a lengthy scene description from Snow Falling on Cedars by David Guterson. It was a description of a boat dock after a severe storm, and it was long. Some of the details were even wrong - but it was riveting, in part for its acute observation of detail, but also because it said so much about the character who was walking through it.
In a sense, maybe "background" is the wrong word, because it implies that something should fade or disappear. In a case like this, the scenery is highly obvious, but it has a purpose other than being scenery. It is serving the larger purposes of the story.
When a piece of world information is at its most relevant, that's when you want it to appear. Maybe you've designed this great alphabet for your language - but since you're writing in English, you don't get to use it to write the story! My instincts would tell me that such information shouldn't be explained, as such, but subordinated to other things. When might people have an opportunity to look at text? And when would its form be important to the story?
In The Lord of the Rings, when Frodo sees letters on the ring, he says "It's some form of Elvish - I can't read it" and Gandalf replies, "The language is that of Mordor, which I shall not utter here." Even if we couldn't see the writing itself, we would still know not only that it's in a foreign language, but that the language is related to Elvish! Sure, Tolkien's having Gandalf explain to Frodo instead of explaining to us, but he's also managed to sneak in the fact that he's designed his world with language families. And that Mordor is bad, and that it will loom large in Frodo's future.
Last - but not least, for me anyway - is social status. The downtrodden are popular subjects for stories, in science fiction as well as fantasy. Support the underdog, because revolutions are fun!
The difficulty is expressing people's low status without having an oppressed character step forth and announce, "The Madugans are an oppressed minority and everybody mistreats them."
That's not how people talk about their own status, because it's too distant and external. Where would a member of this oppressed minority learn the words "oppressed minority"? Maybe from a social worker, if this world has them - but even then, he or she would probably say "We Madugans are an oppressed minority and everybody mistreats us." And who would this person be saying it to? Not to anybody in the oppressed group, because their status is such a normal part of their existence that the statement would be ludicrous in its obviousness.
So switch the announcement into plot form for a minute. To demonstrate that the Madugans are oppressed, take one of them and put them in a social situation where someone trips or hits them, and then insults them. It's better - but not necessarily optimal. The question is, is this a normal experience for a Madugan? And how does the character react?
If the experience is not usual or normal, then think about adding the extra dimension of avoidance. Have the Madugan see the incident coming (they would recognize the signs) and try to get out of it. Then have them try to suppress their own indignation in order to keep out of worse trouble.
If the experience is normal, the Madugan may still see the incident coming - may even expend effort trying to avoid it - but will probably not go into a full-blown rage. Full-blown rage, or even suppressed anger, is stressful and indicative of something that becomes too much, but can have dire consequences.
So what's the result? If you want to portray an oppressed person in a way that suggests they are mistreated constantly, don't actually have them get mad. Have them brush it off compared to what happened last week, or what happened to their friend, or just go "There goes Baron Rompert doing his thing again. Oh, well, better get to work." It will have a very different effect on the reader.
Upcoming posts at TTYU: metaphor, "Show not tell" exposed