One covention that's often played with by writers is the traditional story arc, also referred to as "dramatic structure." It's something that's usually taught in middle school Language Arts classes, then promptly forgotten once the bell rings. And yet, dramatic structure is a major part of writers' lives.
A basic story arc is as follows (see illustration on the right):
Exposition is the opening of the story, and provides background information about the characters, setting, and situation to aid the readers. Often, the exposition sets up what the standard is, then an event occurs in the story to upset the balance. Some exposition is also sprinkled throughout the story rather than dumping it on the reader all at once at the beginning of the story.
Once the standard is changed (in an event referred to as the "inciting moment"), the rising action begins. During this phase of the story, the conflicts are revealed. Whatever goal the protagonist is striving for is complicated by obstacles.
As the complications grow, the story culminates in the climax or turning point. The story changes. Sometimes it changes in a good way (the guy gets the girl) and sometimes in a bad way (the girl is killed by the serial killer), but it marks a significant change in the story.
The falling action follows, and happens much more quickly than the rising action did. After the climactic moment, the story usually wraps itself up. If the climax was a good turning point for the protagonist, for example, the rest of the pieces fall nicely into place. If not, the story unravels quickly.
The story ends in the denouement, also referred to as the resolution. This is the situation witch which the author leaves us, and is a logical conclusion based on the climax and falling action.
This is a basic structure, of course, and can be adjusted to suit your needs. Perhaps you start with the resolution and tell the story in reverse. Or perhaps you start with the climax and fill in the beginning and end as you go along. Regardless of how you use the story arc to tell your story, you do need to know what happens in your story (chronologically) in order to move things around, yes?
An excellent example of needing to know your story arc can be found in The Time Traveler's Wife by Audrey Niffenegger (due to be released as a film on August 14th). In this story there are two separate story arcs (one for each main character), and while they're parallel, they're different from each other. And if that isn't enough for you, the story arcs are broken up and moved around, too. I can't imagine how difficult that story would have been to write if Niffenegger hadn't had a clear idea of how it would've been laid out in chronological order.
A friend of mine (who just so happens to be a writer) has told me that when she comes up with a story, she lays out the plot on index cards in chronological order. Then she can move things around until she's happy with how the story will flow. But she has often told me that it's important for her to know how the story fits together chronologically in order to mix things up. Otherwise, she might end up writing herself into a corner or write something that doesn't make sense in the story. And then where would she be?
Sure, you learn story arc in school. Perhaps you even had to take a short story and plot the main points on a plot diagram. But, as a writer, make sure you know what a story arc is. Make sure you know how your story fits into that arc.
And then, by all means, break the rules.