This would be a fun experiment. Take a simple concept for a book, and ask a handful of bestselling authors to write a story based on it. I'll bet each author will come up with something different, even though the basic premise is the same.
I've read numerous interviews by Stephen King when he tackles the question of where an author comes up with their ideas. He usually comes up with a humorous response to this, but in truth no one really knows where ideas are generated. They just happen. It's something that gets created when an idea starts to grow, almost like a crop.
Don't believe me?
Start with the basic premise of good versus evil. Countless stories are these types of stories, from mythological epics to the fantasy wonders of today.
Then, let's say this is a good versus evil . . . in space.
Mix in a little swashbuckling pirate and western themes, and you get George Lucas's greatest creation: Star Wars.
Break down your favorite stories into pieces. This may give you some insight into the creative process. But I also believe that the key to this is . . . creativity.