The murder mystery genre has become very popular since Agatha Christie. This particular genre need to include an exciting cliffhanger and a storyline that needs to be created in such a way that it keeps you interested in reading.
The first thing you need to do is figure out the basics of the novel and its structure. Note down who will be murdered, the reason, the suspect, where the murder takes place and if there are any witnesses to the murder. Once you nail this information down, you need to go to the next step.
Now you need to expand on those questions by wring down more ideas and expanding on the ones you already have. After doing this, a good idea is to write the opener, where you basically introduce the setting and characters.
Once you do that, you need to write the murder scene. As this is the main subject of the book, you need to treat it with a great importance, and describe it in detail. You might want to hold on to some information in order to introduce it in later chapters, but do what you can to describe the murder as well as possible.
After that, you should try and write the discovery sequence. Who finds the body? A suspect or a random person? Is this tied to the murder, is there any significant information? Integrate this portion into the overall story.
Once you write the discovery, you also need to bring the suspects in. To make the plot as thick as possible, bring as many suspects as you can, and broaden the overall plot with how each suspect might be tied to the murder. You should also add the discovery of new evidence and eliminate suspects as you go along.
Rule the suspects out one by one and, in the end, leave only two or three suspects that give the reader the impression that any one of them could have done it. Once that is done, you should concentrate on the ending, and how you want to finish the story. Will the murderer be sent to jail, or he will live on to kill once more?
A good writer will also proofread and rewrite some portions of the novel at least two or three times. If you want your novel to be perfect, you should try and revise it yourself or hire additional help.
This is very basic advice and professional writers will have much more sophisticated techniques. However, for the new writer the biggest challenge is the first story. Not only is it a challenge to start a story but finishing it is often the most difficult thing. Many stories are sitting out there unfinished. Your first may be a short story, but it’s important to put pen to paper that first time. Good luck!