All mysteries are not created equal
Like all books are not created equal, neither are all mysteries.
I write Cozy Mysteries, so I’ll start there. A few simple rules apply to every cozy. The murder either happens before the book begins or while you’re telling your story. It never happens on the page, that’s a big no-no. No blood and guts please, the readers of these books are a cult following and they will not stand for gore.
No cussing. I don’t even say damn and hell in mind. Bare in mind that even the Teenage Mutant Turtles said damn.
Hard Boiled Mysteries, usually star a professional detective. He’s flawed, not like the perfect gentlemen we met in the last cozy. He has problems, not enough to make you not like him, but enough to make you shake your head at some of his decisions.
He might have been married severaltimes, has a grown kid who always gives him trouble. The ones I have read take place in places you wouldn’t take your Mom, and they don’t spare the gore when describing the murders. You will never have to wonder how they tortured the victim. The writer is more than happy to tell you.
Procedural Mysteries are a step by step account of the murder by a professional. Your protagonist might be a forensic pathology, coroner, or anthropologist. They uncover each clue using detective procedures or maybe scientific ones. They are much more fun to read than try to explain.
Find the killer at all costs. They are most likely in jeopardy, and often are shot, knifed, beaten up or break a bone here and there, which they ignore because the killer is about to escape.
In suspense, the protagonist is the one being hunted. They tend to be more physiological than a thriller.