I have a 2003 Ford Focus, bought used in March of ...

If you would look for any used cars for sale, you should also seek for it history. So you would know on how the old owner have maintained it or how it is serviced. Properly maintained vehicles produce more mileage and proper driving as well.

 You should get your oil changed at its timely or a certain mile (e.g. per 1000 km) that is suggested in your car manual. You should also use the proper tires and tire pressure(for snow tires and vice versa). Properly inflated tires produces less friction with driving for it minimizes the amount of weight it has to drag. and of course, always load your car with the weight that it can or is allowable, and as much as possible, remove things that you wont use that can give additional weight or a bad aerodynamic cause. It is always wise to pay for a timely maintenance or service. and of course, driving your car in the city and the highspeed highways are different. when driving in the city, don't overrev your car, keep it in around 2000 to 3000 rpm. and in traffic jams, always turn off your engine to save more gas.