It sounds kind of obvious, but it helps to listen to the music while you’re at a milonga.
Actually, it helps a lot.
And I don’t mean just be aware of the fact that there’s old-timey sounding stuff coming from the speakers.
Pay attention to what you’re listening to, and when you decide to start dancing, connect your movement to what you’re hearing (I promise I’m not being sarcastic). Respond to the music in your own way, regardless of whether or not you even know the title of the song, who it’s written by, or the name of the person singing it.
And don’t expend too much effort trying to remember what you went over in the last class; there will always be opportunities to practice/improve technique.
Make your partner feel like he/she is dancing. You can’t do that very succesfully unless you allow the music to help you.