Rotor Prep?

I am going to be changing my front pads today. The rotors and pads are pretty much brand new, but ever since I got them changed, I have this really loud grinding sound when coming to a full stop. I am changing the pads to ceramic, and I also wanted to properly prep the rotors because I heard that it would result in a quieter brake as well. Does anyone know the steps for prepping the rotors?