There has to be a blue-white hot passion. Come up with a beginning middle and end. The rest of the book is a journey the writer makes as he ties all relevant pieces together. Every writer comes about their book differently. Some create outlines, some dictate into a digital recorder, some make little notes about characters and storylines. I am one of the lucky few who can "watch" their story develop within their mind's eye. I see things much like a director of a movie - able to rewind, play forward. I'm also able to move my mind's eye to rotate around a scene left, right, up & down. So I'm able to view from all angles the story I am crafting. There is absolutely nothing like being in the "zone" writing non-stop till you finish the chapter. Now I can't do this all the time but when it does happen it is a joy to behold.