Generally (and to over-simplify), fiction writers can be divided into two camps: Outliners and Pantsers. Outliners outline the entire novel before they begin to seriously draft. Pantsers write by the seat of their pants, often with only a vague idea of how the book will end. I have done both, and there something to be said for both techniques.
An Outliner's novel can seem mechanical and contrived. Events occur because the writer needs them to establish plot points, not because they grow out of the characters or the situation.
A Pantser's book can seem loose and shambling. Unless the main character engages readers, they may lose interest, wondering just where this thing is going.
When I teach creative writing, I suggest writers begin by creating a character who wants something in a place (character, conflict, setting). As the character acts to obtain what she wants, you create conflict (conflict = drama). Those actions are the plot.
When I teach mystery writing, I suggest writers begin with the crime and the criminal, then create the character who will solve the crime. In my experience, it is much easier to start with the crime and the motivation of the criminal than to start with the person who solves the crime. If the writer knows who done it, she can plant clues and red herrings along the way to aid or frustrate the detective—and readers.
This of course is neither original nor news. As P.D. James says on her official website, ""I always know the end of the mystery before I
begin to write. Tension should be held within the novel and there should
be no longuers of boring interrogation."
James also advises that "there should indeed be a mystery at the heart of the novel," and I take her to mean every novel. Will Ahab find the white whale? Will Yossarian survive WWII. Will Holden grow up? As it happens, both of my earlier novels include mysteries, but neither is a "mystery" and to be shelved as such in bookstores and libraries because the mysteries are not fatal. And for what it's worth, I wrote both of those as a Pantser.