Great book. I recommend it to beginners and "veterans". Just take what'd really help. Some of the things he says will conflict with your own creative process, and you don't really want that..to an extent. It's not a "how to" book after all.
I want to second this recommendation.
Very good book, and I've had it recommended by more than one professional screenwriter.
Like antiarte said though, there isn't necessarily a universal creative process, and usually you know what works best for you. If you try something and it doesn't work, then it doesn't work. Totally fine.