I cut my teeth playing rock songs on the accordion when I was a teenager and my friends always thought that was extremely amusing. I think that was the genesis of my polka medleys, because every rock song I played on the accordion just sounded like a polka and my friends thought it was funny. So that was a joke that I continue up to this very day.
At this point I've got a bit of a track record. So people realize that when 'Weird Al' wants to go parody, it's not meant to make them look bad... it's meant to be a tribute.
I start with a comprehensive list of all the recent songs that have been big hits - and then I go down that list and see if I can come up with funny ideas for them. I can always come up with ideas, but not necessarily good ones!
I'd like to be able to be more topical and timely and more of-the-moment and I think the way to do that is, instead of waiting until I have twelve songs to release all at once, just to release them as I come up with them.