Make sure to run your air conditioning about every ten days, thus avoiding drying out of the seals, loss of Freon, and clutch malfunction.
Wipe condensation off the inside of the gas cap when refueling. You don't want a rusty gas tank, do you? Try to keep the tank at least half full, especially if the car is to sit for more than two or three days.
Clean off fuses in both the fours and the sixes -- corrosion and condensation can cause problems you don't need.
Clean out the drain tubes at the rear of the engine compartment in both fours and sixes. There are three of these black rubber tubes and they can collect an astounding amount of leaves, pine needles, dirt, acorns, etc.
On fours, up through 1974, move the lever on the intake preheat box to the winter position. Make sure the hose is present to direct incoming air over the exhaust manifold.