Keep your central AC from working too hard with a little help.  The following tips are known as "natural" or "passive" cooling.  Keep eastern facing drapes closed in the morning, western facing drapes in the evening.  Turn your dishwasher's "heat dry" setting off.  Hang clothes on the line to dry instead of using your clothes dryer.  Cook more meals outdoors on the grill to avoid using your stove and oven.