You can regularly take medications such as antihistamines (like Claritin), nasal corticosteroids (like Flonase), or decongestants (like Sudafed) to help treat an allergy to dust mites.
Keeping a clean house is another good way to reduce the number of dust mites in your living space. Replace old, unprotected pillows, duvets, and mattresses with new down or synthetic versions that you've immediately encased in protective covers to prevent contact with allergens. Frequently vacuuming your house and washing items like sheets and towels is a good practice as well.