Sheets should be changed every week
or every two weeks.  Wash mattress
cover periodically also.  Use hot soapy
water and a hot clothes dryer to help
keep dustmites under control in your
home.

Vacuuming your carpet and all floors,
for that matter, regularly, is very
important.  Mopping is essential.  Dust
your furniture each week.  Also,
vacuum your chairs and sofas weekly
to help keep down the dustmites.  
Steam cleaning your carpet or rugs is
another good way to help get rid of
dustmites..  Wash and dry your area
rugs that are washable every few
weeks also.
Oh, those:
House Mites
Dustmites