Clean the Grates

• The interior grates on your floor and ceiling from the heat and air conditioning systems are the last line of defense for dust and dander that's gotten into the ducts. That stuff often gets caught up inside the grates, which means some of it is being released gradually over time into your home when the air kicks on. Unscrew the grates from the walls and sponge them off with household cleaner and warm water.
  
  

Clean the Ducts

• You can't clean your whole duct system the way a professional can, but that doesn't mean you can't do anything about dust and dander clinging to the insides of the ducts near the surface. While the grates are off for cleaning, put your longest hose attachment on your vacuum cleaner, with a brush attachment on the end of it, and vacuum as much of the inner ductwork as you can reach. Follow up by scrubbing with a damp sponge and household cleaner as far inside the ducts as you can reach.
  
  

Change the Filter

• Changing the filter on your furnace is the single most important thing you can do to keep the air in your home clean. Switch it out at least once each season. This is one area where you shouldn't pinch pennies; go with a good filter that not only pulls dust out of the air but also works on pollen and other allergens.