Absolutly. Tyres make a big difference. You need an acurate guage, and pump them up a bit more than Fiat state to reduce the resistance. Having energy saving tyres also helps. Note that there is likely to be less grip available, much like if you brought hard compund tyres. But if you're driving economically then it's not such a problem.
The other thing is, don't brake. Obviously if you need to then do so. But look ahead and adjust your speed without braking in advance. My wife hated me flying round corners in my Punto when she was a passenger. I do it not just for fun, but since it means I don't have to accelerate as much (which uses more fuel), as well as save on braking before hand and its associated wear. In a similar vein, don't accelerate up a hill if you don't need to. Instead lift off a little and then accelerate down the other side. It takes a lot of energy to climb a hill, so use the momentum you have already. Stop-start driving is the worst to get good efficiency, so if in a slow moving traffic jam, keep moving slowly and smoothly, not start, race up and stop.
Drag is also an issue, so don't open windows or the sunroof. Some manufacturers now do special versions with underbody aero stuff to reduce drag.
Final tip: fill right up. Save yourself that extra trip to the petrol station, unless it happens to be on your way normally. I used to be able to get 500 miles from a tank in the summer holidays (less traffic to slow me down). which means less fillings up, with any associated miles to get to the petrol station.
My old trip computer seemed on the whole to overread by a few mpg compared to calculations from full tanks. I kept a log over the 60k miles, and managed to average 50mpg, despite driving with a lead foot sometimes.
