In my case, I stumbled into it. I went to Google I/O and talked to someone who already had written several books for O'Reilly. He proposed the book to them long before I got involved. Honestly, the hacker in me thinks that finding a list of people who have already written for O'Reilly and then seeing if you can help them complete a book in progress might be a good way to get into the oreilly ecosystem.

I proposed a book 16 years ago to O'Reilly and the rejected the idea. So maybe just show up multiple times and you'll get lucky? I think I did.

But once I got "lucky" then I did have three years of hard work for very little money. Be prepared for that!