The most important step in filter improvement is to make sure that all the air that goes through the electric air handler or gas furnace is filtered.
Filters come in different efficiencies that are measured in the percentage of arrestment of particles. Simply stated, what amount and size of particles do they stop? The higher the percentage, the smaller the particle the filter will stop. The other factor that must be considered is the resistance to air flow, or will this super filter let enough air through to allow my system to function properly?
Fiberglass - these are the most inexpensive filters that you can buy. Most people refer to them as the filter you can see through. They stop 15 % of the largest particles in the air. Replace monthly.