First, you have to be patient during the break-in-period, typically the first 1,000 miles or 1,600 km. Apart from keeping your speed under 55 mph, you also have to avoid heavy loads on to the drive train and do not allow your new car to idle for long periods.
Second, buy gas only at reputable service stations. Also, avoid filling up if you see the tanker. As the station's underground tanks are being filled, the turbulence can stir up sediments which can clog fuel injectors and filter - this in turn will cause poor performance that will need repairs.
Third, regularly check and change the oil. There is no single step that will help an engine last more than regularly changing oil and filter. Indeed, nothing will ever destroy an engine faster than neglecting oil-level checks.
