Coppola did an outline for each scene. Each outline had these sections:

1. Synopsis (what happens)
2. The Times (establishing the era; a lot of the details would be described here. Coppola seemed to think you could tell what year it was by what knots men were using on their ties)
3. Imagery and Tone (establishing mood, e.g., the house getting dirtier as the lockdown at the mall goes on and on)
4. The Core (what the audience should take away from the scene)
5. Pitfalls (how the scene could fall flat)

From the Preface, and on the cover:

"When I realized that I was actually going to make a movie out of the novel ‘The Godfather,' I sat down and began to read the book again, very carefully, my pencil poised. Upon that second reading, much of the book fell away in my mind, revealing a story that was a metaphor for American Capitalism in the tale of a great king with three sons: the oldest was given his passion and aggressiveness; the second his sweet nature and childlike qualities; and the third, his intelligence, cunning and coldness.”

Finally, I don't think I made a note above: Coppola had some idea of incorporating Tom's back story via flashbacks during his long transcontinental flight, on the night that he had arrived as consigliere.

Pete, having been spoiled by GFII and its flashbacks, it might have been nice to viewed flashbacks in the GF. However, sometimes not know ing is better than knowing.

This is on sale at Amazon, $41.40 in hardback:

https://www.amazon.com/gp/aw/d/1682450740/ref=tmm_hrd_swatch_0?ie=UTF8&qid=1638227950&sr=8-1

I have also read it and it's a good read, albeit very long, took me like a year cause I kept putting it down then picking it back up. There are some great details as mentioned by mustachepete, and there are a lot of scenes that I believe he wanted to shoot that he just didn't have time for or just didn't make the cut. The only "pitfall" with this book is Coppola's handwriting—I could barely read it, and missed out on a lot of his notes. There are some funny things he writes to himself, I can't remember exactly but some of it is like "Don't fuck this up Francis!"

I do hope there is something in the works like this for GF2 though!