You're going to need to be more specific than just saying "crime novel" to get relevant information. It's a broad genre.
I'm guessing something illegal will happen in it. You may want to include a police character and someone who breaks the law.
Plan the crime, first of all. This may seem a little elementary, my dear Watson (if you pardon the pun), but it is a useful technique - the five W's. Who did the crime? (culprit) Why did they do it? (motive) When did they do it? (time) Where did they do it? (scene of the crime) How did they do it? (method) And then there's more in detail stuff, like how they were found out, etc. This is basically extending on Cogito's idea, but yeah - plan it out first. The rest is self explanatory (write it, then revise).
As an aspiring crime author, my tip is: Make me care about seeing the crime solved. If whether the crime is solved or not doesn't matter to me, then all the details about who/what/when/where/why are going to end up being fairly irrelevant. They are important, no doubt. But only if I care about them. Make that happen for me.
Read some crime novels. Figure out what you feel separates the good ones from the bad ones. Make a plan and see where you go
