1: Make sure your unit has a proper cover and make sure that cover is secured. The cover will help keep moisture and debris out of it
2:Keep the area around the AC unit free of moisture. Ice build-up on an AC unit in the dead of winter can damage it over time.
3: Consider having your AC unit serviced in the Fall by an HVAC company instead of the Spring. Many times they can catch issues before they occur, or fix a problem before the first hot day of summer.