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.
My own personal tastes don't really have an effect on whether song is a parody target or not. But having said that, I try to pick songs that I actually like because I realize that I have to live with these songs for a long time, from when I'm working on them in the studio to possibly playing them onstage for the rest of my life. So I try not to pick songs that I know would drive me crazy.
I'm a music fan, and I can listen to the radio, or music, without thinking, "How am I going to screw this up?" [Laughs] If I'm really actively trying to think of a parody, then I'll have my antenna out, and be a little more proactive about it.
That's a big part of my life - doing things that I'm not prepared to do. Doing things that I don't know how to do, and keep doing them until I get good at them. I always try to put myself out of my comfort zone and out of my depth, and hopefully somewhere along the line I'll catch up.
In fact, when I come up with an idea for a parody I try to resist the urge to Google the idea to see if someone has done it already because the answer is almost always, "Yes, of course they have, they've thought of it!"