I’m a firm believer that you shouldn’t. I know there are several schools of thought on this subject, but all of the others are incomprehensible to me. Trying to read up on how people plot out every action a character takes is somewhat akin to a martian speaking to me in armpit farts; I giggle a lot, but I catch none of it. So, fair warning here, if plotting out everything works for you then keep doing it. Below I make my plea for non-plotting.
Let’s play a quick mind game. You have a very best friend in the world. (If you don’t just pretend you do for this. When you’re done reading go get one.) For simplicity let’s call this friend Billy and assume it’s a guy. Your very best friend in the world has known you a long time, and vice versa. Seeing that you two have spent countless hours together, it’s a safe bet to assume that you know that person pretty well. Now imagine that Billy, your best friend, just came to you and said, “I robbed a bank, and I need help.” How would the situation proceed from there?
You don’t know? Billy wouldn’t do that? When you write a book you are ideally writing about the most interesting thing that ever happens to your character. So assuming that your protagonist is as predictable as Billy, how would being thrust into a new situation affect him? Until you see Billy in that situation, you can’t say for sure. You can guess and make a plan based on that, but when they time comes something different might happen. As a writer, you need to be open to that. If you say Billy would turn himself in it would make for a short and boring story. If you then find out Billy robbed a bank to pay the ransom for his sick mother’s cancer treatments, we have a better story. Or you might find out that mild mannered Billy is the grandson of the world’s greatest bank robber. (‘Bank Bustin’ Billy the First) Old grandpa taught him everything he knows, and he finally got the guts to test it out. If you plot out every detail ahead of time you aren’t telling a story, you’re making a chart.
My characters have surprised me on several occasions throughout the two books I’ve written. I always started with a vague beginning, and a vague end. I flesh out my characters and the world, I make a rough outline, and then I dig in. Things always change once the ink starts flying. Ben, the protagonist of Darker Shadows, did something that changed the whole second half of my first book, but the ending remained the same. Something happened to a character in my second book that totally altered the second half. On both occasions my mind was blown. It was one of those times when I had to get up and step away from the keyboard for a moment to let the gravity of the situation sink in. When I write a story it’s like reading it for the first time. A lot of the things that are going to surprise my readers surprised me as well. When I started writing I didn’t think that would be the case. It’s made the work more fun than I thought it would be, and that’s saying a lot.
Hell, maybe I’m totally off base with this one. If you can plot out every detail ahead of time and still write a great novel, go nuts. I can’t. I’ve tried and it comes across as too stiff. I need to shed that grid map and have some room to breathe, otherwise it stops being fun and interesting. But even if you’re a plotter, consider this: It’s impossible to really know another person, and the same is true for your characters. Even when you’ve written out a novel’s worth of back story on them they should still be able to surprise you. I’m not saying your entire book should be a crap shoot, but if Billy finds a way to get away without getting caught you should let him, even if you had planned to throw him in jail at the end. He is your best friend after all.