To keep your long term maintenance costs low, there's no better place to start than by scheduling regular oil and filter changes.  Most vehicle manufacturers recommend changing the oil once a year or every 7,500 miles in passenger cars and light truck gasoline engines. However, that once a year, 7,500 mile oil change is for vehicles that are driven under “normal” driving conditions which is only about 20% of drivers. Nearly all of us fall under “Severe Service”  driving conditions - frequent short trips (less than 10 miles, especially during cold weather), stop-and-go city traffic driving, driving in dusty conditions and driving at sustained highway speeds during hot weather. For this type of driving, which is actually “severe service” driving conditions, the recommendation is to change the oil every 3,000 miles or six months. For maximum protection, most oil companies say to change the oil every 3,000 miles or three to six months regardless of what type of driving you do. The purpose of the oil change is to remove the harmful contaminants that have accumulated in the crankcase and to replace the depleted additive package in the used oil. If you go beyond this recommendation your vehicle could be dumping more unburned fuel into the crankcase which dilutes the oil. This causes the oil to break down and not adequately lubricate the engine and vital parts. So if the oil isn’t changed often enough, you can end up with accelerated wear on your engine and parts and all the engine problems that come with it including loss of performance and fuel economy, as well as, increased emissions and oil consumption.

The oil filter should be changed every time the oil is changed because up to 3/4 of a quart (3/4 of a liter) of used oil remains in the filter when only the oil is changed. This contaminated oil immediately mixes with the clean oil and contaminates it. It is cheap insurance to make each change a complete one with both new oil and filter.  When it comes to air filters, it is important to use a high quality air filter that holds up under our extreme driving conditions.   Note that quick lube shops will often user lesser quality oil and filters.  

If you don't drive your car much or at all (7500 miles a year), then you probably want to change oil every six months anyway. If you are storing a car during the winter, then change oil before storing it and change oil when you bring it out of storage.