Writers all have different processes in the creation of a book. Some appear to have lightening fast skills that result in a finished work every couple months. I'm in awe of them.
My process goes something like this.
Idea=write the scene.
Muse suddenly has more I must write now!
Reread above material and spend two months rewriting it.
Show critique partner.
Rewrite beginning because it's stupid... I always end up rewriting the opening...Still no ending.
Finally find ending.
Send to critique partner.
Critique partner uses kind, gentle words = rewrite ending coz it has to make sense.
Send to editor
Month later hear what she noticed needs fixing, of course she's right and I wonder why I never saw that.
Rewrite the parts that make sense only to me and the flying monkey that is my muse.
Send to editor.
It goes on, but you get the picture. For me, the editing process is like sculpting the story. Cutting away the excess to reveal the image inside.
So it takes me a while to drag the story I want to tell out. Some of them I think I know before I start writing, but then things just seem to happen on the page as I go and the story is quite different when it tells itself.