Define a Beat
A beat sheet is just a collection of story beats. Beat is a word that gets used in a lot of different ways in the writing process. Here, we're using it to mean a discrete element of your story. It's probably closest to a scene, though there will also be some connective tissue between scenes that you can safely skip over at this stage. Imagine yourself describing a movie to a friend who hasn't seen it. You more or less instinctively break the story down into beats when doing this. Here's an example: Bob calls the cops and they go back to the office, but the place has been cleaned out. The furniture's all gone, nobody's there, the building super says it's been vacant for months. The cops think Bob's just looking for attention and tell him not to bother them with this again. That would be a beat in your story. All those elements--bringing the cops back to the office, finding it empty, the cops thinking Bob's wasting their time--belong together. And taken as a whole, they've moved your story forward.
Lay out your key structural beats. Gather the index cards, open up a new file on the computer, whatever you're going to use, and lay out the key beats that will form your story's structure. One of the nice things about a beat sheet is that you don't have to do things in order. At the same time, you want some boundaries so you're not just scattering stuff randomly around the page. There are five key beats to start with:Inciting incident: The event that kicks the story off. In Star Wars, this is when the story enters Luke's life. He sees the message from Princess Leia. First Act turning point: This is the moment when the hero leaves his old world behind to enter the world of the story. In Star Wars, the empire kills Luke's family and he leaves behind all he knows and goes off with Obi-Wan Kenobi.Midpoint: The center of the story. This raises the stakes and usually changes the hero's goal. In Star Wars, it's when our heroes find themselves trapped on the Death Star. Before they were just trying to bring the rebels the plans and find Princess Leia. Now they're in serious danger and their goal is to escape with their lives.Second Act Turning Point: This scene is the opposite of your climax. If you're going to have a happy ending, the second act turning point is bad news. Alternately, if your hero's going to fail, the second act turning point is where it looks like he's got it made. In Star Wars, it's the death of Obi-Wan Kenobi. How can Luke succeed on his own, without his mentor? All seems lost.Climax: This is the dramatic end of the story. Though there may be some things to wrap up afterwards, this is what the story was leading to. In Star Wars, it's where Luke blows up the Death Star and saves the day.
Now that you've got the basic skeleton of your story laid out, you can put some flesh on the bones. You need to add beats to connect those elements. With this part of your beat sheet done, you can focus in on one segment. For example, what happens between the inciting incident and the first act break? You've got the beat at the beginning and at the end of that part of your story. All you need to do is figure out how your hero gets from one to the other. Start writing beats. You can let yourself run free at this point--you'll fix anything that's not right later.Keep on doing this until you've taken your hero from start to finish and have a rough draft of your beat sheet.
Count the beats. Once you have the beats taking you all the way from start to finish, you can pull out and look at the big picture. The first thing to notice is the proportions of your story. The beat sheet should just "look" right. The midpoint scene should be in the middle, of course. And the first and second act turning points should be roughly the same distance away from it. Ideally, the first act turning point would be about a quarter of the way through the story, and the second act turning point about three quarters of the way through. In other words, those three beats divide your story into four roughly equal segments. You don't have to be too precise about it, but if you've got a very short second act and a really long third act, you might want to take another run at it.
Based on your overview in Step 4, add new beats, drop ones that seem unnecessary, rearrange beats, move them from one act to the next. Your beat sheet should be a working tool. Use it as a guide when writing, and let it evolve as you make creative choices and become more familiar with how your story's going to work. A properly done beat sheet is never written in stone. But at the same time, it can help you decide what you need to do next, and reassure you that your story is on track.