Service your car regularly. A well tuned and maintained vehicle will perform better and more economically.
Keep your tyres at the recommended pressure. Under-inflated tyres can increase your fuel consumption by 10% or more.
Make sure you check your radiator level every fortnight and top it up if necessary. Use coolant, not water, as this will retard corrosion and save later repairs.
Keep the battery on full charge. A constantly discharged battery will not see out its full life.
Keep your engine clean. It makes servicing easier and reduces the risk of grease and grime build-up hampering cables and other moving parts. Fix small mechanical problems before they become larger ones. You can save expensive repairs that way.