Don't run your ac too cold; when the ac is in Celsius, 26 or 27 is more than enough.
When you leave a room for more than an hour, switch the ac off (air circulates constantly in and out of the house).
Buy and run (ceiling) fans they can cut your cost with 50%, as you don't need to set the ac that high.
Run the acs in the rooms you don't use for a half an hour every week or 2 weeks, just to keep them in a working condition - you might also want to run them to prevent mold.
Do not run the ac in the room with your computer too cold, as when you turn it off vapor can spring from metal parts.