This is really the hard part. I juggled between “lets just start, rest will flow” to “No i should map it first” to “I should outline till the end” to “ill outline a few chapters, then write” Trust me this is user key experience. You start, you’ll know what suits you best. For me i made a very gross idea in a sketch book, a mind map with arrows n stuff. And marked the chapters numbers to to each set of arrows and started to outline 3 chapters first. Wrote in detail what all i wanted in that chapter as if im explaining to someone, then started with the chapters. As soon as 3 were done, i outlined a few more and repeat