With the end of the semester, I went back to work on my whimsical children's novel (no joke, I am currently writing the 32nd draft of the first chapter). And I realized that one of my problems was that my first chapter contained both: a) a pretty atypical setting; and b) an event that was, for that setting, fairly out-of-the-ordinary. And this sets up an almost impossible challenge. It means that you simultaneously need to convey the setting well enough that readers know what events are ordinary for it, while also describing a big out-of-the-ordinary event.
The problem, though, is that if your setting is weird, then the way that readers understand it is by observing the things that happen within it. For instance, if the first chapter of my novel was set in my escalator-world (a world made entirely of moving escalators), then the way the readers would understand the rules of escalator-world would be by observing how they function in the first chapter. However, if I open the novel with the escalators all screeching to a halt, then no matter how much I have the characters panic and react to the screeching escalators, the reader is never quite going to get it, because they've never had the opportunity to see the escalators functioning normally. Thus, any story that's set in a weird place needs to have a chapter or two of events that are ordinary (for that place) before the big, crazy stuff happens.
The problem there, though, is that it still needs to feel like something is happening. It can't just seem like the novel is spinning its wheels until its time for something to happen. And that means that those ordinary events need to contain enough tension to propel reader interest and, additionally, they need to somehow suggest the shape of the big, dramatic events that are going to come along shortly.
On the other hand, if you open your novel in a place that people understand very well (an airplane, a suburban public high school, a typical pseudo-medieval fantasy land), then you can open up with something weird happening on page one.
So to recap:
It's okay to start with an unusual event in an ordinary setting: For instance, if in the very first page of a high school novel, one student jumped on another one and then started trying to eat his brains and everyone began to panic, it wouldn't be that confusing at all, because you would immediately understand it as something that's out of the ordinary.
It's also okay to start with an ordinary event in an unusual setting: For instance, if, on the first page of a high school novel, one student jumped on another one and then started trying to eat his brains out and then the second student pulled out a pickaxe and bashed the first student in the head, and then the janitor came out and swept up the blood and gore and doused everything with ZombAway, then you wouldn't be confused, because you'd be like, "Okay, this is zombie high school world, where this kind of stuff happens all the time."
What's confusing is when you have an out-of-the-ordinary event in an unusual setting: For instance, if, on the first page of a high school novel, one student jumped on another one and then started trying to eat his brains out and then the second student pulled out a pickaxe and bashed the first student in the head, and then everyone in the school started clapping and praising the second student as the best zombie-killer to ever walk the halls of that school and the big-titted cheerleader sidles up to him and is like, "Oh gawd, I love how you bashed that zombie. If it'd been anyone else, then that zombie would've killed us all." Then you'd be like...uhh...what? Exactly how unusual are zombie attacks? What is going on? Do students expect zombie attacks? Or are zombie attacks unusual? None of this is making sense to me!