Unless you consider yourself a great dancer, pick a song with a rhythm that’s easy to follow. Keep in mind that you can learn your first dance choreography to any song but it is always easier and faster to learn to a song that has a beat. That’s one of the reasons more and more couples these days tend to choose modern songs to dance to

Check out my list of modern first dance songs:

I will be happy to advise you in your song selection. Keep in mind that if I see you struggling with matching the steps to the rhythm of the song, I will suggest changing the song.
Of course, sometimes the reason you’re messing up is the fact that the steps are too advanced. That can always be adjusted. However, when the entire routine is performed off beat, then there’s a problem. I simply know that if you keep losing rhythm while practicing in class, you won’t magically dance flawlessly on your big night.