A routine service will generally cover the following areas; engine oil and oil filter change, checks on the levels of coolant/brake fluid/power steering fluid, checks on lighting /signalling/brakes/clutch, reading of onboard auto diagnostics, air filter/spark plug replacements. These checks will generally cover MOT and safety requirements and because of the complexity of today's cars are best carried out by manufacturer trained mechanics. A further breakdown of service detail will outline the benefits of some of these areas.
Engine oil and filter change lifecycle will vary according to the oil type used. Modern oils have moved from mineral to semi-synthetic to fully synthetic. Synthetic based oils will generally last longer than the old mineral type and offer a greater range of protection to the engine, an example of which is Castrol GTX Magnatec that can protect the engine from the start due to magnetic properties built into the oil. A professional car servicing garage will use the oil recommended by the vehicle manufacturer.
Fluid levels for the coolant, brake and steering systems will be checked and topped up as needed as part of any service but these should also be checked by the car owner on a regular basis under routine conditions. Lack of engine coolant can result in major engine damage to anything from the head gasket to the big ends (this will mean engine replacement!). Lack of brake or power steering fluid will also cause problems with control systems which are obviously paramount for driver safety.
Almost all modern vehicles will have onboard electronics which may include auto diagnostic functionality. A properly equipped service garage will be able to link into these systems and gain information of any intermittent or impending problems that may have occurred since the last service thus giving an extra layer of security and oversight.
Air filter replacements are necessary at anything from 25,000 to 50,000 miles and are also dependent on environmental conditions. A clogged air filter will restrict air flow to the engine thus reducing power and fuel consumption. Spark plugs are one of the least expensive parts of the engine but probably one of the most critical for optimal engine tuning. Some spark plugs are claimed to have life spans of 100,000 miles, general manufacturer service recommendations will specify replacement every 30,000 to 50,000 miles. Even with long life spark plugs they will need to be removed and cleaned regularly to ensure they don't seize into the engine.
These are some of the reasons you should carefully select a car servicing garage with fully trained professionals who will have the equipment and knowledge to optimise the performance and safety of your car.