I get this question quite a bit. I don't know why. I'm not a very disciplined writer, by any means. But heck, if you want to know my methods, I'll tell you.
First, I start with the ending. Generally like this:
The sun shone over them then, and he watched with tears pouring down his face as Cleopatra rode off on a llama. And in that moment, he knew he would love strawberry jam forever.
And then I think, "holy shit! that's an awesome ending! I need to somehow create a story that allows me to get there!"
So then this happens:
Another sex scene
And so now I have all these unrelated parts that are swimming around. But I have to link them together! And sometimes I cannibalize bits from other stories, that I realize fit more with this new story.
Oh, and don't forget this:
Super witty line I thought of as I was drifting off to sleep, and really doesn't go with anything, and I can't really remember it but I'm gonna try my damnedest to fit that in here too. Even if I have to write whole new chapter to make it work!
So by then I have several pages worth of story, but not in any sane form. This is where it takes me forever to actually post. And why it takes me months to sometimes update stories that are multiple chapters, because I'm trying to arrange all these pieces like a jigsaw puzzle that's missing all the edges.
But finally I get impatient enough into writing
Which finally links up all the other bits, and then I'm done! I am absolutely staggered by people who actually do outlines and, like, knew what was going to happen the entire time! How do you do that?! Is it magic???!!!
Coincidentally, the method described above is also what I did for writing my term papers when I was in college.
Except those had more sex.