Whenever I talk to classes in schools, I often emphasise the importance of planning out your stories before you start writing them. Here's the sheet on which I've planned out the plot of my next book (which doesn't have a title yet)...

Yes, I know, it's a total mess. But there's a lot of thought and note-taking gone into this total mess, I assure you. Anyway, by the time the story is finished, it'll make a lot more sense than it does now! I hope.