Like a check-up for the car; check and adjust anything that needs adjusting, like idle mixture, belt tension, valve clearance, and also change fluids and lubricants that need changing, the engine oil, oil filter, sometimes the brake fluid, sometimes the ATF or transmission oil. Also, check ignition components against specks, and replace stuff that's off, like the plugs, wires, coil or rotor. Other than an underhood inspection and check underneath the car and tires, that's about it.