One of my writing friends came to me recently and confessed they didn't know how they were going to end their book. I generally have the opposite problem, I know how I want it to end but not how to get the story there.
I usually start with an idea. Mary Sue Smith gets sucked into Neverland and meets Peter Pan the third. Usually that idea suggest certain scenes, Mary Sue actually getting sucked into a trans dimensional literary portal, meeting Pan at the point of the sword, Captain Hook as a conflict, lost boy acceptance, defeating Hook, Mary deciding how to live happily ever after. I'm a sap. I like happy endings, or at least bittersweet ones.
Those scenes (which are the most fun to write) get me started in the rough draft. The trouble comes in connecting the two. I try to write chronologically. If I get stuck I will skip over scenes with a minimum of narration, putting something like write a cool fight scene here or Mary needs to learn to waltz here. I write the next scene. Then I can back track. Mary needs a sword to fight the pirates therefore I need to get one to her in the scene I skipped. Mary needs to face inner demons personified in Hook, therefore in the earlier scenes we need to give her inner demons.
Each action should have an after effect and a series of events that led up to it. Although it may offend the artistic senses, writing a novel requires a great deal of logic. If the story doesn't make sense then all the flowery prose in the world will not save it.