2015 Mazda 6 Auto, driven in the city on a stock tune was getting around 8L/100KM when new. Fast forward a few years, I now live in the country. It is tuned on 91 octane. With hypermiling techniques, I got between 6-6.8L/100km depending on how aggressive I was driving, winter/summer blend fuel, and the amount of stops. Now, on my last tank, I averaged the lowest ever of 5.3L/100km.
Drive slow. don't be constantly accelerating up to speed, or slowing down, unless you truly need to. especially on a cold start is when you will waste the most fuel and accelerate drivetrain wear. be gradual as you get up to speed and maintain a more or less average rate, even if it is slow. don't ever force the engine, especially when climbing hills. Take advantage of the downhills to get up to speed.