Wall-mounted split
Rinse the filter every few weeks during heavy use, and keep the outdoor body clear of leaves and clutter.
Ceiling cassette
Wipe the visible grille often, and book a coil clean before the smell or weak airflow sets in, since access is harder once water spreads.
Centralized and ducted
Watch for uneven cooling between rooms as an early sign, and have the ducting checked for damp ahead of the wettest months.
Portable and window
Empty the water tray often, and clear the filter so the small build is not overworked in the heat.