It's really hard for me to pin down where, exactly, I start a story from, but I definitely think it starts with the world. I'm a big believer in starting with the world as a whole, and develop it until it shares its stories with you.
For example, the world that the Maradaine books are set in, I had been building and growing that world for years. Years. And I had a real problem finding the story for a while, in no small part due to wanting to craft a story that matched the scope of the world I had made. Which? Mistake.
Here's a thing I've learned: stories work better if they are in a setting where you can tell there is a richer tapestry being woven all around it. That doesn't mean you have to do crazy, masochistic worldbuilds for every book (but you CAN), but... you want to give the sense that the world around your story also has so many other stories.
I'm not going to name names or point fingers, but there are plenty of stories-- big, notable stories-- where it's very clear that the world was crafted around that particular story. Which is fine! Nothing wrong with it. But then you'll see attempts to tell more stories in that world, and it's clear the scaffolding was not built to support that.
So that's my method: first build the sandbox, and THEN start to play.
Though with the next book I'm writing, The Velocity of Revolution, I'm pushing myself out of the comfort zone a bit by not quite doing that. Quite. It'll be a different process. But I'm excited for it.
All right, back to the mines.