Change air filters often with inexpensive pleated filters. Airflow is the most important thing a homeowner can control in regards to their air conditioning system. Please look at this research done by the University of Central Florida Research
Keep foliage away from outdoor equipment. Foliage within two feet of outdoor equipment can impact the amount of air flowing across the outdoor coil which affects efficiency and equipment longevity. At least once per year, clear vines out of coil and trim plants to allow for this two-foot breathing area.
Treat for pests around outdoor equipment. Ants and mice can cause a whole lot of expensive damage. They can chew wires, short electrical circuits, and make a mess of the controls in your air conditioning equipment. Ideally, treat at the beginning of the Spring and then again once each month until the Fall. Repairs needed from damage caused by pests are never covered under manufacturer warranties.