Rather than fill up my mp3 player with a bunch of unlistenable crap from the local pop station like some people, here are my guidelines for making a playlist for those cartrips when it's my turn to pick the music.
-Nothing over 4 minutes, even if it's my favorite song (at the moment). Nothing's worse than sitting awkwardly waiting for Erotic City to finish up.
-No dance/repetitive music. It gets real boring real quick. Hot Chip, I'm totally looking at you. And I'm dancing, because your music is awesome, but not good for straight up listenin'.