A compelling mystery story gets the reader connected with the crime almost immediately. When you start writing, be sure you are clear on what the mystery is and how you will solve it at the end. A murder, typical of most good mysteries, will have circumstances, evidence, a feasible method, and maybe even a motivation that may not become clear until later.
Develop a small group of characters, several of whom will become suspects, even if they appear to be helping or cooperating with the investigation. If you take time to develop the actual acts leading up to the crime at the beginning, you engage the reader in the development of the mystery and the event itself. Alternatively, the murder may have already happened before the start of the book. In that case, take the reader back on a journey and let them experience the event itself, but not exactly how and who did it. Then they will want to read on, find out why it happened and make sure the perpetrators are caught. Make the crime itself unique. Instead of bludgeoning the victim over the head with a crowbar, try formulating a deadly and difficult to trace poison.
Have a hero, a detective, a private eye, or another unwilling but intuitive player who leads the investigation to solve the mystery and even the score for the victim and his/her family. Find an event or experience from the past that uniquely motivates the hero to be involved. Experiences may include familiarity with poisons, a lost loved-one in similar circumstances, or something about the victim’s family that create a strong pull.
Create suspicion in every scene throughout the book. Leave the reader wondering why a character did or said something, or reacted oddly to events, or appeared to intentionally mislead the inquiry to hide something else they don’t want revealed about them. The reader should not easily determine who is not telling the truth, or hiding details or misdirecting the investigators. Keep track of the outline of your storyline so you don’t lose track of your story as you follow each of the lies and misdirection of your suspects.
Borrow a technique from television detective shows. Zero in on a prime suspect and begin a heavy investigation of that person. Midway through the story, the detective and the reader become convinced you are on the right track. Then have the story twist and turn to reveal the real villain, and his/her motivation, late in the book.
Describe the setting for the story and base it on real-life places, people, and events. Helps reader to associate easily with story and adds level of believability to get them hooked. Drop hints and clues along the way. Make sure some of them are bogus clues, so you are assisting the redirection process and adding to the mystery.
Think about yourself and friends when developing characters. You all have flaws, some of them may be huge, and yet you successfully navigate life. Similarly, make your characters unique with strengths and flaws or quirks that get in their way. Add unique quirks. I know someone who is so afraid of snakes that just the mention of the word “snake” sends her into convulsions. Find your own unique quirk and your character will be more likeable and entertaining.
Once you have your manuscript written and you’ve done your own first round of editing, have a small number of key reviewers read it, one after the other. Be prepared to make major revisions and additions after each review. Then send the revised copy to the next one, not back to the first one, you are not trying to engage in a complete rewrite conversation with on individual. Now that you have the mystery solved, write on!