Filters have a efficiency rating called MERV, ( Minimum Efficiency Reporting Value). The higher the MERV rating , the cleaner the air and the better the equipment protection. Control dust, dirt, and pollen with high quality filters and/or air cleaners.
Warm indoor air contacting the evaporator coils will condense causing moisture to collect and drip. In most units, a plastic pipe carries the water outdoors or to a floor drain. Algae and bacteria growth can clog the pipe, many people will use a pan treatment to retard the growth of algae, etc.