Step 1: Destroy Dust Mites
As much time as you spend in your bed, dust mites, the active ingredient in house dust, spend even more. In just 2 weeks, a new bed can have 2 million of these tiny critters shacking up in it. Though you can't see these allergens, their feces is a huge cause of itching, watery eyes, nasal congestion and coughing.
Zip your mattresses and pillows into dust mite covers. Similar to regular bedding covers but less permeable, these seal the dust mites in so they suffocate and are kept clear of your space. Two things to look for when you shop: pores that are under 10 microns in size (to keep the buggers locked in) and fabric that is 100% cotton, if possible, so it's breathable and cool.
Wash bedding in hot water (at least 130° F) to kill dust mites.
For items that can't be covered or easily cleaned such as upholstery or curtains, sprinkle or spray on a tannic acid solution (found at allergy control retailers) that neutralizes the proteins caused by dust mites (and pet dander) so they won't trigger an allergic reaction.
Step 2: Keep It Clean
Besides dust mites, your home is filled with other free-floating allergens such as pet dander (skin flakes from your cats and dogs) that find their way into your nose, throat and ear passages causing a scratchy throat, watering eyes, sneezing and congestion. Regular cleaning will keep them from building up.
Dust, sweep, and vacuum at least once a week, including curtains, blinds and vents. Whenever possible, use HEPA (high efficiency particulate air) filters, which take up even the smallest microns of dust and trap cat and dog dander.
Wear a dust mask when you clean to keep from breathing in the very allergens you are trying to contain. Masks are cheap and you can find them at your local drug or hardware store.
Use a particle-trapping dust cloth instead of a feather duster. It will pick up the dust rather than just sending it in a flurry into your air.
Hold the line on humidity. It's not just mold and mildew (both allergens in their own right) that thrive in moist, warm environments. Dust mites are big fans, too. Buy a hygrometer to measure the moisture in your home, and if necessary, purchase dehumidifiers to tackle moisture trouble spots.