Use a good quality motor oil of a known brand, which carries the API classification SG or SH. The proper viscosity of the oil depends on the climate and temperature your car is operated in.
Change the oil at the intervals recommended. If the vehicle is being used in severe service such as trailer towing, change the oil at more frequent intervals.
It is especially important that the oil be changed at the proper intervals in emission controlled engines, as they run hotter than non-controlled, thus causing the oil to break down faster.