I'm slowly working my way through my first edit of the first draft of the Darren Dash science fiction book which I'm currently in the process of fine-tuning and assessing. (See my post of February 8th for more on that.) I wrote the first draft well over 20 years ago (maybe even closer to 30 -- I can't check at the moment, because my documents from thatg time are all in storage), and I'm tweaking almost every line, adding or subtracting words, reshaping sentences. In the next draft I might end up having to make structueral changes to the overall shape of the book, if I find that such changes are necessary (I'm hoping they're not!!), but for now I'm working on it on a line by line basis, trying to improve on each and every one if I find them lacking. (And most are -- I've learnt a LOT since I wrote this as a young, budding author.)

But, for all the changes I'm making, the bones of the story are there, which makes this much easier than if I was starting from scratch, trying to flesh out an idea which I'd had a couple of decades ago. I always advise young writers to GET YOUR STORY WRITTEN. Don't worry about quality when you're working on a first draft. You'll have loads of time to go back afterward and rewrite and edit. But when you're starting with a story, the most important thing is to GET IT WRITTEN. Get all your ideas down on paper. See how the characters develop. Plot it out, then write it out, and get to the finishing line as swfitly as you can. Then take a deep breath -- I usually allow myself a break from a book of at least a few months, sometimes years, on occasion decades. Then, when you're ready, return to it, behave as if you're an explorer charting virgin territory, chop your way back into it, and see what you find.

[The accompanying drawing, which neatly summarises all of the above, was drawn by Austin Kleon for a blog post a few years ago covering ground much the same as this one: https://austinkleon.com/2018/04/30/first-drafts/ ]