This is a guide that I mostly use for mysteries.
Let's be honest, most crimes/mysteries you read in novels have a 'theme' so to speak. But the question is raised,
"Where do I get a theme and how do I use it?"
What I do is I remember or research a recently talked about or a very easy to remember moment or tale in my childhood.
For example of what I'm talking about
For Moment: Cinderella's shoe fell off and Prince Charming finds it and returns it to her(eventually).
For Myth: The boogeyman.
Now that I have a theme, the first thing I do is to 'modernize it'( If it is old or unnatural, try to make it so that it is believable or do-able in the time period of the novel/short story) . Then I develop a summary of what occurs, then I work on how the characters know who the killer is. Maybe a few notches in the investigation and then I reach a climax, after the climax I resolve what happens( maybe explain the motive if I didn't already) and put the bad guy in jail and end the story with either a cliffhanger or a re-occurence that started the plot or the character living 'happily ever after' or etc.
A kick in the reader's teeth is to name the characters after the theme. (For Cinderella's case, naming the major character, a female, Cindy or the outrageous naming of the character CINDY R. ELERsly/ELLAR( when the capitalized letters are read, you can clearly make out Cinderella) or giving the character a trait that resembles the moment (Like Cindy having a knack of losing her shoe or the person being the boogeyman has a job as a child services officer.). These are good for punning.
Now these plots I have created using this method as I write this guideline without any previous thought.
The main character, Cindy R. Ellar (pun intended.), is mistreated by her friends and family. But with the help of her guidance counsellor, she gains enough courage to ask someone out to prom night( Let's say the person's name is Chandler for this guide's sake.). Cindy's habit of losing her shoes kicks in and Chandler returns them to her. She then becomes friend and advances to lovers with Chandler. But then a bizarre murder of Cindy's mother, then her two snotty sisters, then friends etc. plagues her and she and Chandler take matter into their own hands. After analyzing the clues, she discovers that Chandler has an obsession over her and stumbles upon a cove/hideout which he has pictures of her. He then meets her and she suspects him to be the murderer, he admits and fights her, he is either killed or sent to jail. In the end, she finds out why he loved her and she then lives a normal life until she receives a letter...
The main character, unknown only as Fisk, investigates a murder of troubled children that is a raging epidemic across the US. It seemed that the children were apparently scared to death. During one investigation, one child managed to wound the killer and the blood trail led to the closet, then Fish is stumped as to how the murderer escapes. But a sibling of one of the victims tells him that it was the boogeyman, but he doesn't believe that. After a recent murder, Fisk managed to trap all suspects who were there at the time. After using a trick dealing with security tape and the number of guest that were in the house, Fisk manages to catch the murder, a middle aged man child service officer( who was close to his youth group, girl and boy scouts, anything that deals with children). After catching the criminal, he helps the children cope, tie off lose ends, kiss the girl etc. The end.
1)When in the process of creating the story plot, DO NOT worry about evidence yet. Just focus on the plot itself and the evidence will follow.
2)Keep in mind that if it is multiple crimes( like in the examples), that they must have similarities that display similar Modus Operandi.
3)Remember, naming or giving traits to the characters after the events is a good way to start off character creation, but don't go overboard with it or do too many characters like them. Some character can just have no relation to the event whatsoever, it makes the story feel a bit more natural.
4)This method can be applied to different genres, for example The Cinderella plot could easily become a Thriller if Chandler sent her gifts and showed his stalking of her more often and she was getting paranoid. Just because it is a great help to creating a good 'themed' mystery doesn't mean it can't be a thriller either.
5)Remember, THE MURDER/PLOT HAS TO BE RELATED TO THE MYTH/MOMENT!
6) The examples may look rushed or imcomplete, but this is a SKELETON of what you will be writing. You can flesh out every little detail when you are actually writing.