4. The hero or heroine does not always have to be competent. Remember that they can have inner conflicts? A detective can be an alcoholic, drug-dependent, or on the brink of retirement and is slowing down. The protagonist can be ineffective at the beginning and eventually comes to terms with his shortcomings. The hero/heroine finds a way to resolve it for the sake of a cause that is greater than him/her. On the other hand, the protagonist can be difficult to work with and is not popular among his/her peers. Everyone hates the main character, but they couldn’t get rid of him/her because this protagonist is one of the best crime solvers in the force. As a rule, it should never be easy for the protagonist. Oftentimes, the villain gets back at the hero/heroine to inflict revenge, and this adds tension.

5. A shocking event is an ideal way to open the story. A young girl found murdered by the river. A terrorist saying his last prayers before putting on his vest planted with C-4. The element of time pressure must be always present. A crime solver who has the luxury of time can become passive and uninteresting. The plot becomes unexciting. Their efficiency and brilliance must be tested by time constraints.

6. Premeditated crime makes for complex and intriguing problem-solving. Two drunkards stabbing each other to death in an argument is typical.  A hacker who tampers with a government website and is found in the process is too easy. The complexity of a crime determines the array of subplots that can branch out. Each of these subplots can present thrilling revelations or events related to the main crime.

7. The killer or the principal suspect doesn’t always have to be on the loose. He could be arrested immediately or be murdered in the first quarter of the novel. However, this should only give an illusion that the crime has been solved. Let’s say the serial killer has been incarcerated at a maximum-security prison. The series of murders continues with the same murder pattern attributed to the imprisoned killer. This creates a new problem for the hero/heroine. Does the killer have an accomplice? How many murderers are acting at the convicted killer’s behest? The story takes a new turn. 

8. The crime must be unpredictable. If the protagonist easily understands the killing pattern, then he is not heroic. Things must go awry for the hero/heroine because the circumstances and the villain dictate it to be. Why would a villain allow himself to get caught by making it easy? 

9. Involve the reader by giving him access to all character viewpoints. This adds an element of excitement for the reader. The reader knows something--an action that the protagonist and antagonist are planning against each other. The tension will build from the reader's verified fears.

The success of your mystery, detective, suspense or spy story largely depends on how well you can create a convincing villain to the point that readers bite their fingernails while reading. Give the reader a first-person experience as if the killer is right behind them. Give the shock value to whom it is due.