Back in the day, you took your car in every 20-30,000 miles to have her “tuned up.” That meant Goober at the local filling station changed your oil and filter, air filter, fuel filter, spark plugs and wires, distributor cap and rotor button, replaced/adjusted/filed your ignition points, and maybe replaced the condenser. That was considered by most a full service tune up, guaranteed to deliver top performance from your ’56 Chevy inline 6 for another 20k or so. Nowadays, service intervals for vehicles are 100k miles or more and the process is different for every vehicle.
With electronic ignition modules, COP (Coil On Plug) ignition systems, more efficient fuel systems, and platinum and iridium spark plugs, the days of the “tune up” are long gone even though the term has stuck around. The best thing you can do for your vehicle is to stick with the manufacturer’s recommended services which are usually listed in your owner’s manual. Again, they’re all different so make sure you check for each vehicle you own. For instance, a late model Toyota Avalon has a spark plug replacement interval of 100k miles or more, but a late model Dodge Ram has a spark plug replacement interval of just 30k miles. The difference is largely due to the type of spark plug electrode material used (copper vs. iridium or platinum).
The modern service recommendations usually include a timing belt (if equipped) as well. If the vehicle has a replaceable fuel filter (many don’t!), it should be replaced at 100k unless the manufacturer recommends a shorter interval.