Let’s be frank here: every writer is going to have a unique approach to writing a book. I’m not going to sit down and say “you have to do it this way!” For one thing, that would be bad advice. For another, it would be wildly hypocritical. I’ve written three novels, and each was approached in a wildly different manner.
As most writers probably know, there are two general types of writers when it comes to novels. There are “plotters” and there are “pantsers,” or, as George R. R. Martin famously put it, “architects” and “gardeners.”