According to the National Wood Flooring Association, a hardwood floor should only be waxed when buffing no longer restores the floor's shine. The time between waxing varies, depending on the traffic the floor receives, but usually averages out to once or twice per year.
There are specially designed floor cleaners made to fix a wax finish that has dirt buildup or discoloration. These wax cleaners should not be water-based, but rather a solvent. To protect and maintain the wax on a hardwood floor, never use a cleaner designed for vinyl or tile floors and never damp mop a waxed floor. Too much moisture will cause damage to the wax and possibly to the wood underneath.