Since I'm starting to plot a new novel, I thought I'd use this space to go over how I do it. (Partly so I'll get it all straight in my head--I seem to forget completely, every time, how to start a new project!)
First, I take advantage of a couple of excellent courses I've taken. Margie Lawson created a class especially for a group I belong to called Guppies (the Great UnPublished online chapter of Sisters in Crime) and I start my plotting with her excellent guidelines. She has inexpensive lecture packets of most of her courses available on her webpage, http://www.margielawson.com/index.php/lecture-packets. I can recommend them highly! I also use a course I took from Mary Buckham on synopsis writing. Her method of doing synopses finds all the plot holes! You can find Mary at http://marybuckham.com/, BTW.
But here's the part that's original to me, my timeline spreadsheet. (If it's not original, then I don't remember where I got it. Sheesh. If you want to take credit, go ahead.) When you're writing a mystery, it's important to know where everyone is all the time. The characters have a tendency to skulk about in the shadows, but I have to hunt them out--the writer has to know what they're up to!
It's a simple spreadsheet. Across the top, I label the columns with the names of the important characters, and sometimes a few unimportant ones I want to keep track of. Except for the first several columns. The very first column is a list of the events of the story, the scenes, the clues, the happenings. These define the rows. The second column, for my benefit, is the date and time of the event. I use the third column to put what thread this event is concerned with, a clue, a red herring, a suspect, and I sometimes color code them. Sometimes I put the chapter number in the fourth column, then the character columns start. The protagonist owns the fifth column, since she's in the majority of the scenes.
As the scenes unfold, I note, beside the scene and under the character, what their role is in the scene--what happens to them, or what they're thinking or feeling or planning. If one of them gets dead, I color the rest of that column a dark color, usually gray. Since the first murder is an important defining point in a mystery, I can tell at a glance if I'm before or after the killing. I can also tell at a glance when some minor character is getting too many scenes, or when a major player has been out of the picture too long.
I use another worksheet to keep track of how I've described the characters, making sure their eyes don't change color, or a short person doesn't suddenly become a six footer, but that can just as easily be done in a word processing program. It's just handy for me to have it all together.
That's it! My nifty spreadsheet. I have it open most of the time I'm writing so I can insert the action as it unfolds. If you've ever written fiction, I don't have to tell you that, no matter how carefully a plot is structured, it changes. One of my characters in the last novel jumped from minor to major character, changed his name three times, and told me, in no uncertain terms, that HE was the romantic interest. What could I do? I adjusted the chart.
If someone can use this to keep things straight, let me know!