Clean the forced-air furnace and air conditioner filters regularly.
When the air filter is dirty, it will slow down air flow into the system. This will make your system work harder to keep you warm or cool. This is a big waste of energy and money.
A clean filter will be more efficient and prevent dust and dirt from building up in the system. This dirt can lead to expensive maintenance or even early system failure.
Check your filter every month, especially during heavy use months (winter and summer). If the filter looks dirty after a month, change it.
At a minimum, change the filter every three months.