For me, it all starts with the characters.
The good ones usually show up in my head and stare at me until I decide to keep them. I'll kick things around in my head for a couple of years (yes, years. I tend to be slow like that. Maybe I'll get faster as I gain more experience in writing and story-telling in general), listen to a lot of music that "sounds like them", and generally just let them reveal their stories to me in their own time.
Once I've soaked up "the feel" of a character for a while, I'll try to puzzle out what the most interesting story about them would be. What would be the most important part of their life? What would the worst possible situation for them to be in? I find that interesting/horrible situation, and then put them in it. Then make it worse.
I outline. Lots of bullet points. I re-arrange things as I go.
Then I write. I am finding that if I put TOO much detail in my outline for a given chapter, it falls flat. I need to free-flow for my prose to work. As long as I know generally what the chapters about, I can make it work.
And most importantly, I make sure my main character arcs are SET and WORKING before I write anything.
That's just me. I have yet to finish a novel, so... we'll see if it actually works!
One more thing. I'm a firm believer that stories are not created. They all live out there -- somewhere -- in the ether, and its just my job as a storyteller to prepare myself in such a way that I am able to hear them tell themselves. It's my job to "tune" my aentenna -- so to speak-- to their frequency. Once I hear the story, I need to translate that to words or to film or whatever. That translation is where the craft of learning to write, or the craft of filmmaking, comes into play.
I know that sounds hokey, possibly even pretentious. But it's a very real thing to me. I've found that shifting my brain to think this way has made a big difference in the quality of my stories and writing.
These are not my stories. I just write them.
(Huh. That's going into my signature. Starting....now)