If you don't have a dehumidifier, get one. Less humid air actually feels cooler to the skin. Air conditioning lowers humidity and removes dust and dirt by moving the air through the air filters. You will get a significant saving by having a dehumidifier.
Step2
Check your filters, check your filters, check your filters. They should be changed once a month during peak use--every two months otherwise. Filters become clogged with dirt and the system must work harder to do its job. Mark it on your calendar to remember to do it!
Step3
Buy a programmable thermostat. Program it to get cool an hour before your arrive home. This will save money and once it is programmed a no brainer.
Step4
Shut the doors to rooms not in use and once you turn on the air, keep it on. The more your home keeps out humidity, dust and heat, the more efficient your unit will run.
Step5
Replace your air-conditioner with an energy efficient unit. The more efficient unit should pay for itself with lower energy bills!