One needs to think about the sources described above. It is always better to control a problem by identifying and then fixing the source. In the case of badly worn carpeting, replacement may be desirable. Badly soiled carpeting needs to be vacuumed and cleaned more often. Attic insulation can be kept out of ducts by sealing joints tightly with duct tape.
Filters are a last resort.
The typical furnace filter is primarily designed to collect lint. One changes filters because heavily soiled filters increase resistance to airflow. Changing filters often will not ensure a clean house nor will more efficient filters.