I write and write and write, and then I edit it down to the parts that I think are amusing, or that help the storyline, or I'll write a notebook full of ideas of anecdotes or story points, and then I'll try and arrange them in a way that they would tell a semi-cohesive story.
I'm very analytical, I'm very precise. I mean, I don't write for kids.
I know now that everything I write, I'm going to put out, and I'll have to live with it for the rest of my life.
So that's why one of my rules of parody writing is that it's gotta be funny regardless of whether you know the source material. It has to work on its own merit.