Not so much preventative, but I do have a tip. Insure the electric cooling fans in front of the condenser are operating as intended. If the fans fail for some reason, the a/c will still work fine while moving, will work quite poorly while stopped. The lack of airflow while stopped will cause much higher pressures inside the system, as heat is not being removed. (Remember pv=nrt from high school?) This will stress the compressor, manifold hoses, condenser, and of course the o-rings in the system. Eventually the entire system will fail. Sometimes an o-ring gives up the ghost, releasing the refrigerant charge. Sometimes the front seal on the compressor begins leaking, which can result in eventaul seizing of the compressor.
Anyways, on a warm day the electric fans should run at low speed (or cycle on and off) after a bit of stop-and-go driving.