Tune-up is a very vague word. It could mean a simple oil change to more involved, less frequent maintenance. This would be a more thorough "Tune Up" here...
Ensure proper fluid levels:
- Change oil change w/new filter
- Engine Coolant flush (we talked about coolant pH decreasing with age leading to issues in another thread). When to change depends on type of coolant used. You can test the pH to check the acidity, but old coolant may also be contaminated and have decreasing cooling abilities
- Check power steering and brake fluids for proper level
- Check transmission fluid for proper level. A flushing of the fluid is recommended on some vehicles. On others it is not. Regardless, maintaining a proper level of oil fluid is obviously necessary.
- Check wiper fluid level

...and wiper blade health (though this should be apparent driving)
Belts/Hoses:
- Inspect serpentine belt (and others if applicable) for damage
- Inspect hoses for bulging, cracking, or other future issues
Ignition:
-Spark Plugs, gapped correctly of course (~30,000 miles)
-Wires (if necessary, if you replace one you should replace all)
-Remove corrosion off battery terminals- this crap builds up inevitably over time and can lead to starting issues.
**If your plugs are a B**** to replace, i.e. annoyingly difficult to access sometimes it's easier just to replace the wires while you're in there, especially if you think they'll need to be done by the next time you change your plugs. They're not particularly expensive. My old WJ Jeep (V8 engine) was a pain to do plugs on, and you wouldn't expect that being a V8 or a Jeep.
-Checking for burnt out lights- sometimes it's possible to miss small parking lights or license plates lights. CT cops love pulling people over for a single license plate light (most cars have 2).
Filters:
-Air Filter (for sure)
-Gas Filter (a good decision)
-Interior Air Filter (if applicable, optional really, may just need a cleaning)
Tires:
-Inspect tires, check pressure, wear, and damage
-Balance and rotate wheels
Cosmetic Stuff:
-Wash car and wax to preserve paint
-Clean inside/outside of all glass (I suppose this is beyond cosmetic)
-Condition leather if applicable to extend life- prevent cracking, creasing, and other wear
-Remove brake dust to prevent it from burning to your wheels
-Mothers 'Back to Black' for that fading black trim you may have
That's all I can think of right now.