The natural way is vinegar and baking soda. The easy way is purchasing Lime-a-way.
Lysol power scrubber in the blue trigger spray bottle for soap scum is awesome. Wet and forget shower is good for keeping it clean once you get it cleaned off.
Waxing the tiles (not the grout) with a good quality car wax and a soft clean cloth that has not been laundered with fabric softener will facilitate future care of your tile.