I start off with a three song warm-up, as the Zumba corporation suggests (focusing on simple moves like step-touches, grapevines, etc. with a few fun moves for flare). For these songs, I tend to try to use two songs that are currently popular, and at least one with a Latin feel. In the past, for example, I've started with Lady Gaga's "Applause" and went into Pitbull's "Back in Time" (which I make my class sing - they love that). For the third song, I use something with a hard-driving beat and that is easily countable (as I focus more on toning moves - squats, standing crunches, etc.). Right now, I'm using Britney Spears's "Work Work" (the clean version of course).
The rest of the class I divide into two parts. The first half I devote more to songs that are Latin-inspired or World, switching between different tempos, intensities, and styles. For instance, I would start off with a salsa-inspired song like "Culebra," followed by a merengue song like "El Amor" and/or a Cumbia, then a reggaeton song like "Descontrol" or "En Sus Marcas Listos Fueras" and a Masala Bhangra tune like "Indian Moonshine." I also try to bring in one hip-hoppy/clubby song at the end for a short battle (splitting the class in half for the end of the song; always fun, they really like going at one another;)). I've liked using "Sweat" by Casely and "Work" by Lil Jon in the past. This section is usually made up of between 5-6 songs, depending on whether I have a full hour or 55 minutes.
As a break between the two class sections, I do a squat song. Whatever you want, as long as it's fun ... and killer.
For the last section, I use three harder songs (a Latin-flavored pop song, a reggaeton battle, and a powerful closing song, whatever floats my boat), one standing-ab song (also bringing the heart-rate down), and a cool-down. Currently, I am using Enrique Iglesias's "Turn the Night Up," Don Omar's "El Conteo" (a full-song battle), and "The Floor is On Fire" (by Pitbull, Lil Jon). For standing abs, it's always fun to use Shakira or Kat DeLuna as inspiration. The cooldown is up to you, something low-tempo and easy to follow.
Have fun planning your own!! Let me know if you have any questions (and if you haven't tried Zumba yet, get out there. Anyone can do it:)!!!). A/J