I began the way nearly everybody I ever heard of - I began writing poetry. And I find that to be quite usual with writers, their trying their hand at poetry.
If you blithely do what you do and you're good at what you do, and try to be a decent person, you can succeed.
So in the first draft, I'm inventing people and place with a broad schematic idea of what's going to happen. In the process, of course, I discover all sorts of bigger and more substantial things.