There are, of course, an infinite number of ways to write a book. In these articles I’ve been outlining how I do it, because that’s what I know to write about, but there are no binding rules, no arbitrary guidelines. That said, there are some structural… suggestions that can benefit almost any writer. Stories can have more impact when they follow a basic architecture. Even here there are variations. I know people who stick to the twelve stages of the Hero’s Journey. I know writers who like five act structures, because that was good enough for Shakespeare, dammit. Personally I work with the three act structure, which is the simplest and, I think, the most effective.
You can think of three act structure as the beginning, middle, and end of your story. Or the setup, the buildup, and the punchline. I like to think of it this way;
ACT I: Oh, look, I’m in a forest.
ACT II: Oh, no! I’m getting lost in this forest!
ACT III: Oh, look, there’s a way out of this forest.
Perhaps I should elaborate.
Act I of any story is the shortest. Sadly, it also has to do the most work. This is going to make up about 25% of your total word count, but it needs to do the following things: establish all the main characters of your story, as well as the setting, pace, and tone. Establish the problem of the story, as well as the stakes (what happens if the problem is, or isn’t resolved). By the end of act one your protagonist must be stuck on a path that leads to a final conflict. That can mean that the evil mustachio-twirling villain has kidnapped their boyfriend. It can also mean your hero has realized they have a drinking problem, and they’re headed for rock bottom.
Act II is the longest act, the most fun, and absolutely, without question, the most dangerous. Act two is where you develop all your clever ideas, where your protagonist tries out various solutions to the problem (none of which, of course, work). It’s where you have room and time to explore the setting and build character arcs and do all the fun parts of writing… and if you make a misstep, your story will go right off the rails. Act two is a time of steadily increasing tension, modulated with (occasional) moments of relief. All that exploring you’re doing? Imagine a maze with one exit, and all the various paths through the maze MUST lead to that exit, even if they wind a little bit. It’s way too easy for something to go wrong in act two which then sabotages the most important act…
Act III is longer than act one, but shorter than act two. It’s the most laser-focused of your story’s sections and often the easiest one to write–although, perversely enough, it can also be the thing that kills you. When act three begins the die is cast. Your protagonist knows (or thinks they know) how to solve the problem. They have good, compelling reasons why they MUST solve the problem. The stakes have never been higher. The protagonist works at nothing else past this point–they will sacrifice anything to resolve the story. The antagonist (whether you have a bald, cat-stroking villain or a natural disaster like a mudslide) is moving steadily toward an easy win and they have every reason to be confident. Then the magic happens. Somehow (you’d better know how) the protagonist gets the better of the antagonist in a surprise twist and the world is set to rights. Yay! Then you can have a denouement that’s as long or as short as you like (I prefer super-short), and you’re done.
Of course none of this happens by magic. You need to outline your story (if only in your head) before you start writing. You can save yourself a lot of trouble that way. There’s an old bit of writing advice I’ve found to be almost universally true: if there’s a problem in Act III, it’s a problem with Act I. Go back and look and you’ll see you didn’t set something up properly.
I’ll add two corollaries to this chestnut. First: If there’s a problem in Act I, it’s a problem with Act III. If you have trouble making your protagonist believable (could a four year-old really build a rocket to escape the Mars-beasts?) it’s because they’re the wrong person to face down the big antagonist at the end of the tale. If the setting feels off or boring, it’s because it’s too small to hold the ending.
And finally: if there’s a problem in Act II, it’s because you’re writing the wrong story. Act II is for exploration. Often times, you can explore so far you find yourself in a completely different story–maybe the story you really wanted to write in the first place. If this happens, don’t despair! Either go off and write that story instead… or put it aside, somewhere safe, and go back and find where your act II maze got side-tracked, and fix it!