This is a question I get asked during every estimate and after every job is completed.  The most important part of caring for your hardwood floors is to stay caught up on your dry sweeping.  Keeping the small dry particulate soils up will help prevent the tiny scratches in the polyurethane coating.  Occasionally the floor will need to be damp mopped.  The key word here is damp.  When you damp mop the floor the area cleaned should be dry in just a few seconds.  If you use a hardwood floor cleaner make sure it doesn’t say it will restore luster or shine.  Any product claiming to restore luster or shine will leave a heavy residue behind and prevent recoating the floor in the future.  Also, when using hardwood floor cleaners, less is more.  We typically over apply cleaners, and this too, will lead to residue, or haze being built up on the floor.  This is why I like to use the PolyCare Hardwood Floor Cleaner.  This is a concentrated cleaning solution that you add to your warm water.  This will be prevent over application of cleaner and prevent a buildup from forming on the floor.  Most importantly keep in mind that a hardwood floor cleaner is just that, a cleaner.  When a floor doesn’t shine after cleaning, it is time to put a fresh coat of polyurethane down.