Check the condition and charge of the battery. Extreme cold and extreme heat will cause a no start
Flushing the cooling system and change coolant once a year will keep the cooling system in good shape and prevent corrosion and deposits from building up.
Keep it clean
Aclean car is a happy car. While washing the outside of the vehicle is obvious, most everything the vehicle ran over can also get stuck to the underside. Hosing off winter salt and road grime will prevent rusting of key parts.
Check and change the oil. No single step will help an engine last more than regular oil and filter changes will.
Transmission and Diff oil
Change out transmission and differential oils. These fluids must be changed according to service intervals. Always use transmission fluid or gear oil of the recommended type and viscosity.
Everything with moving parts needs grease to survive. Ball joints and Steering components especially, need to be greased every time you change your oil.