I use Naptha prior to touching up a playfield with paints. It cleans and removes all previous wax so the paints adhere better.
For playfield cleaning; I've had no luck with Simple Green (maybe the newest formula is weak). I tried not to use Mill Wax based on some threads, but it cleans great. Mill Wax cleans really well. It will turn a white cloth black from all the dirt and grime it removes.
I then give 2 coats of Maguire Carnuba wax. Letting last coat dry over night.