Dance Paradise

Simply finish dancing to 20 songs. The songs must be unique, meaning you can't dance to one song over and over again. If you're playing through the career you'll get this easily, but each song you play in multiplayer and free mode also count towards this achievement.

You can also keep track of which songs you've played. From the "Main Menu" simply go to "Scores" and whichever songs you have scores on you've finished.