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.
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.
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!"
I tend to enunciate pretty well. It's always seemed that my voice is one of those voices that people can recognize pretty easily - which has been a bit of a drawback for some characters because you're supposed to lose yourself in the character, but sometimes people look at a character and go "Oh, it's 'Weird Al.'"
There's a lot of different ways that a song would be a challenge to parody. There are a lot of songs that would ostensibly be a good candidate for parody, yet I can't think of a clever enough idea. Some songs are too repetitive for me to be able to fashion a humorous set of lyrics around. Some songs flat-out just don't work creatively for me.
It's hard to really articulate what the parameters are that make one song parody-able and another song not, but if I can come up with a good enough idea for it, I go for it, and if not, then I have to move on.