You'll want your first plot point to hit around page 100, the second at 200, the darkest moment at 300 then you'll have 50 pages to wrap up and resolve the book.
What's a plot point? It's a significant event within a plot that digs into the action and spins it around in another direction. Your hero is going along nicely trying to reach his goal, when you throw in a twist, change direction, make it impossible for him to keep going. Be mean to him! Make him sweat. After all, conflict is what moves your story forward and keeps the reader turning pages. Your book will be a series of "what ifs."
Whew, he finally figured out what to do now he's moving forward. He's pretty sure he knows whodunit, why and with what. He's going to save the fair lady and she's sure to fall in love with him. Then you come to about the 200 page mark (this isn't exact so to don't sweat it. Page 194 is fine) it happens again! You put another elephant in your hero's path and once more, he's stuck - or so it seems. Everything he thought was true is wrong. Naturally, he'll find a way to keep going.
Just when he's almost achieved his goal we come to the darkest moment at around page 300. All is lost, there's no hope of the hero ever getting to his goal. It's seems, impossible, but of course it's not. Now you have about 50 pages to pull your hero out of his terrible mess and get him to the end. Our hero solves the crime, gets the reward, or the woman, maybe both, the promotion, whatever. The reader can give a sigh of relief and close the book with a happy smile on his face.
As I've said before, you want to have lots of conflict in your book; it's what keeps the reader reading. My first writing teacher explained it to me this way.
"The reader of your book has popped into bed and wants to read just one chapter before she goes to sleep, but she finds she can't put the book down! Suddenly, it two in the morning, she has to get up in a few hours to go to work, but she HAS to read, just ONE MORE CHAPTER."
That's the kind of book you want to write, don't you?
Along the way you'll have to plant red herrings, introduce characters who MIGHT have done the crime, situations that challenge the detective. We're lucky today to have the internet. With the click of a mouse, you can find a super, undetectable poison to use to
kill someone or find out how long it takes a body to go into rigor mortis - and come out again.
Now that you have an idea on how to plot a book, I can hear several of you saying, "But do I HAVE to?" No, you don't. I don't. Sue Grafton doesn't nor does Tony Hillerman. Like me they get an idea, sit down and write. You might want to try that method too, but I'll tell you from my experience, it's easier in the end to have at least the semblance of a plot. If sit down and write your book from Chapter One to The End without a plot, you will find yourself going back again and again to put thing into the book, like red herrings or characters. Those who write by the seat of their pants spend more time writing the book than do those who plot. So, you've got to decide which is the best way to write, but do try plotting first. It's easier to keep track of everything that way too.
I think it was Alfred Hitchcock who cautioned, "If there's a gun on the wall in chapter one, it damn well better be fired by the end of the book." That's a paraphrase, but close enough. What does it mean? We've all seen it. Sally walks into the spooky old house and sees.....a butcher knife sitting on the kitchen counter and....is that blood on the blade????? We have the bloody knife in the back of our minds because it's been pointed out to us. We read, and read, and keep thinking okay, where's the knife? We get to the end and find it had nothing what-so-ever to do with the plot! That knife isn't a red herring unless you can explain somewhere along the line why it's in your book. Maybe the cook had been cutting up chickens - fine, but give us that information at some point or we'll be angry when we finish the book and realize how much time we spend thinking about that bloody knife and it had nothing to do with the killer.
Please, don't bore your readers. That's easy to say, I know but it's amazing how many books I read that start with a bang, have interesting characters, a dynamite premise but still sag in the middle and become boring. Why? Probably there's not enough conflict. I know I keep coming back to that word, but conflict is what makes your book sing. It's what keeps people reading. But first of all, it's what gets an editor to buy your book.
Alfred Hitchcock said, "Drama is life with all the boring parts left out."
So, when you're writing your book, remember to leave the boring parts out. I'm still amazed when I read books where Bill and Sally have been talking on the phone and Sally says, "I have to tell you something but it has to be in person. Can you come over to my house?"
"Sure," says Bill. He gets his coat from the front closet, shrugs into it and goes in search of his keys. Outside he walks to his car, gets in and starts the engine. It's only seven
blocks to Sally's house, but there's construction on Maple Lane, so he decides to go the long way over to Chandler and down Nobel Drive. He parks in front of Sally's and walks up the sidewalk and knocks on the door.
Have your eyes glazed over yet? My fingers almost froze just writing this! It's boring. Instead do something like this:
"Bill dropped the receiver into the cradle and hurried over to Sally's house."
Now you've accomplished the same thing with many fewer words. We don't care nor do we need to know how Bill got to Sally's house. And yet I still read books who give me a long description of streets and avenues, cornfields and whatever. I don't care. Just get your characters from point A to point B and leave out the boring parts.
What about time? Same thing. You can end the chapter or section with something like:
"I love you," Bill said and took Sally into his arms."
The next day Sally stood in the kitchen, a frilly pink apron tied around her tiny waist, cooking grits for Bill.
Voila! No boring parts.