Tune-up requirements vary greatly from vehicle to vehicle. The age of the vehicle, the type of driving it is used for, the quality of fuel used and of course the manufacturer and options on the vehicle all have an effect on over-all wear & tear, and need to be considered if expecting the most from performing a tune-up. Typically, a tune-up will consist of changing the spark plugs, performing a series of tests on the ignition, fuel, starting and charging systems, and confirming efficient engine operation. In many cases, it is also advisable to replace ignition wires and, where applicable, distributor cap & rotor at the same time, to prevent unnecessary starting & driveability problems between tune-ups. 

Tune-up or spark plug replacement intervals can be as little as 6 months on much older vehicles to as much as 160,000 kilometres on some late-model vehicles using platinum spark plugs and high tech engine management systems. Recommended intervals may be found in the maintenance schedule of your owner's manual. Bear in mind, though, when following these recommendations that they can't take into consideration every factor that is going to affect spark plug life. Hard acceleration, high speed driving, stop-and-go driving, infrequent or short trips, using low-grade bargain gasoline and other driver-controlled factors may shorten the expected life span of even the most high-tech spark plug.