Choose a story that you have a solid pitch for. Find a mentor text that is similar in structure (not necessarily topic) to the book you want to write. Type or write out the author’s words and number the spreads; Analyse the structure. Look out for page turns. Compare the end with the beginning.
Now aim to give your story a similar structure and shape. Start by roughly plotting key events into 12 spreads.
Where do we meet the initial conflict? Where will the climax be? How does the tension build? Where will it be resolved?
Don’t worry too much about ‘how’ your character will get to each point. Think more, ‘what they will be doing/ feeling and when.’ It’ll act as a map that you can throw out of the window once you’ve got going! When you have plotted the key events in a form that suits you (notes, table, stick men or something else) prepare to share it for feedback from a writer friend. (In numbered paragraphs).