In your service record book it lists what should be done at each mileage so you could look there as a start. Also check what has been done at previous services to see if anything has been missed. Standard things are likely to be engine oil and filter change, diesel filter change, pollen filter change, lights/brakes/steering/suspension/tyre checks (parts replacement not included), fluid levels. Others may include air filter change, brake fluid change, anti freeze change, drive belt and cam belt changes