Clean filters monthly. Not all AC filters are disposable, and disposable isn't better. For the same price as disposable filters Target sells cleanable ones that last for a very long time. At the beginning of each month I hose the filters and air dry them. Within a few hours they are back in place and back to work.
Suck the drain ports with a wet dry vac twice a year. Not doing this can result in clogs, which result in leaks in your house and problems with the AC unit.
There are plenty of tutorials guiding you through cleaning and maintenance of the AC system and condenser. I've never tried this myself, and don't plan to - it's pretty far out of my comfort zone. Whether you clean these machines yourself or hire someone to do it once or twice a year, know that an ounce of prevention is worth a pound of cure and that this routine maintenance can save a significant amount of money in the long run.
In summary:
- Filters cleaned or changed monthly (the 1st is a good day to do it, change the calendar, change the filter)
- Drain ports sucked twice a year, at least
- AC and condenser maintenance performed once or twice a year
