A small 4 cylinder pulling a large car will have pretty bad mileage if you push it hard. The lower you keep your revs and the less your injectors are open, the better the mileage you'll get.
Some other stuff to make your best better:
Check all tyre pressures - too high or too low can make your them wear out too fast, or make your mileage worse.
Don't use your heater on defrost or floor. That will run the compressor (for whatever reason) and will eat up your mileage. Just use the panel setting to keep warm, and defrost only to clear the windows.
Get rid of all excess weight. ie - extra speakers, junk, etc.
Clean all the snow off the car.
That's all I can think of at the moment.
Best of luck. I once got 807Km in my 5.0L on 85L of regular. Contour's personal best is 500+ on 50L of premium.
