And yet, it's not unusual that a poorly written book gets a decent movie adaptation. Sometimes it's not even a good plot OR well written, sometimes a book is just popular and the execs cash in on its popularity.
I'm thinking things like Da Vinci Code, 50 shades, Twilight, neither of which (the books) are particularly good or tasteful or whatever, but they were very popular, appealing to people who normally don't read books.
You're definitely looking for something other than the writing and even the plot. For example, the novel "The Firm" had a ridiculous ending but they fixed it for the screenplay.
I dropped of a book to this guy that I had just finished called "The Hotel on the Roof of the World," and he later told me that they optioned the author. Unfortunately the film never got made, but if you read it you'll see it has the bones of a really nice film.
How did he get that job? I imagine you have to prove you have good "taste" for what makes a good movie... I imagine some difference from what makes a good book
I think it was a combination of right place/right time, knowing everything about film-making (and you're right, what makes a good adaptation) and was just a naturally cool, interesting guy, so that everyone who met him just liked him.
It didn't last forever. The last time I saw him was one of those wild random coincidences. I was visiting Cannes during the festival (as a tourist) and ran into him on the Croisette. We went for coffee and he told me that he had become a television producer.