I've never done anything to them. If you hear a lot of grinding coming from rotor just wash out with hose or pressure washer. Pretty much maintenance free.
That is the best thing to do. Ecspecially if you have drilled rotors, they will trap a lot of debris and wear pads fast.After heavy mud riding, I take the front tires off and spray the front disc's with a hose, just to get all the mud and junk out of them. I spin them around a few times until I dont hear any more grinding from them.