Clean air filters.
Check air conditioning filters monthly to either clean or replace them. This will help the unit run more efficiently. Better yet: buy a permanent filter that can be washed and re-used. This will save you money over the long run and keep all those disposable filters out of landfills. If your unit is outdoors, check to make sure the coils are not obstructed by debris, plants or shrubs.
Clogged filters can make electric bills skyrocket and eventually cause extensive, expensive damage to your air handler.