Regular maintenance is a must. Like any piece of machinery, if it is not 'tuned up' periodically, it will not run efficiently or last as many years.  Below are a few items you may be able to perform yourself to help keep your system running efficiently.

The number one item to check is your filter. Be sure it is cleaned or replaced regularly. During the heavy months, changing it once a month is a good idea. I also recommend using a disposable filter. They are cheap enough and filter the dust better than some permanent style filters.

If you are able to, inspecting the duct system once a year and making minor repairs with some duct tape would save you some money.

Spring time is a good time to clean the condenser coils. Be Sure the power is disconnected. Spraying the coils with a garden hose will remove the dirt from the previous year. Sand and other debris gets sucked into the coils and will cause the unit to run inefficiently. Also trim back any plants or foliage at least a foot away for proper air flow.

Cleaning evaporator coils is a little tricky and care must be taken.

Depending on how mechanically inclined you may be, oiling the motors is a must. If you are not sure of yourself on this, don't try.

Hopefully you will have many trouble free years of Air Conditioning. You can also expect to make a service call. Know the company you are dealing with, get second opinions when repair costs will be high and if you suspect a fraudulent company, turn them in!