What kind of book? Non-fiction, fiction, general topic, etc.? That might make a difference. I wrote a science fiction about 20 years ago and am finishing a project management book now, should be working on it instead of spending time on FR. Those two have very different needs.
Nonfiction, it’s all experiences that have fallen into my lap. I’ve been hesitant to comment much here even though I’m a longtime lurker. I have had personal interaction with many individuals discussed here. While employed I have been very hesitant to share but I’m recently retired