1. Get a digital thermostat, one you can set your AC (or Furnace) to go on and off at certain times. Its good to have it turn off when your not at home or when your sleeping.
2. If you have rarely used rooms in your house close the duct vents in those rooms.
3. check your filter and make sure its clean.
4. check all incoming pipes and make sure they are insulated properly, 40 cents worth of insulation can save you hundreds in the long run.
5. Use silver tape on all your ductwork from the furnace on up, NOT duct tape but the thin metal tape, the more air gaps you can block the more efficient it will cool your home and that will result in savings as well.