What, apart from actually driving ? Joking apart, urban driving (lots of stopping and starting) will use more fuel than cruising steadily down the motorway. Also speed is a factor (eg 56 mph is reckoned to be the optimum speed for minimum fuel consumption). Having the air con/climate control on will use more fuel, as will carrying loads on the roof. Your style of driving makes a difference - lots of revs and sharp braking are going to cost more than smooth acceleration and simply taking foot off gas pedal ! Other than that, maybe you've got a fuel leak somewhere - can you smell anything ?