I was a huge fan of 'Mad' magazine when I was 11, 12, 13 years old. I'd scour used bookstores trying to find back issues, and I'd wait at the newsstand for a new issue to come out. My life revolved around it.
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.
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.
When I was a kid, I thought I was going to be an architect, because when I was 12 years old I had a guidance counselor that convinced me that that was the best career choice for me.
I make charts of songs that are good candidates, good targets, so to speak. Then I try to come up with ideas for parodies. And 99% of those ideas are horrible.