Changing your motor oil and filter on time is the easiest and best way to maintain the health of your vehicle.
Check your tire pressures regularly; under-inflated tires give poor gas mileage and significantly reduce the life of the tire as do over-inflated tires which can also cause your vehicle to have a stiff and harsh ride.
Make sure you are familiar with the service interval requirements of your vehicle. Many cars have timing belts that need to be replaced at 60k or 90k mile intervals. Failure to replace this belt on time can cause thousands of dollars of damage to your engine. .
If your check engine light is on, you will not be able to pass your Smog test. Have your car diagnosed and repaired before you are due for Smog.
If there is rain in the forecast, than by all means wash your car before the rain! When your car is clean, preferably with an added coat of spray wax, the rain will simply roll off your car and your car will stay quite clean through the wet weather. But if your car is dirty, the rain will mix with the dirt to form a corrosive mixture that not only makes your car even dirtier, but will also over time damage your car’s paint and finish.