I think a writer's notebook is a good idea, but when I had one, I kept losing it. I am not very organized about things like that. So I keep a notebook in my head, kind of. They never work out for me. I start first with character development.
Outlines do work for some people, though.
It takes different times for different books. The shortest was three months and the longest was three years. One book I thought about for several years, took notes, and then eventually wrote it. I like to write long stories. My first 12 books are being reprinted by a new publisher, so I've reread them and written afterwords about them.