Agree with the above post-ers about calculating gallons consumed and miles actually travelled. Offhand, suggest you should be in the 20-25 mile per gallon range, depending on your mix of highway and city miles, winter warm-ups in the driveway or other extended idling periods, etc.
The standard stuff always applies - make sure the car is in good mechanical tune, no 'check engine' lights, don't carry unnecessary weight in the trunk or elsewhere, keep tires aired up to spec, and perhaps best of all - use a light foot on the gas pedal.
Not a big fan of the add-on stuff, one type of which is mentioned above. Haven't heard of any astounding improvements in mileage from real-world, uncompensated purchasers. Plus, any savings in fuel have to be weighed against the cost of the accessory - which may end up taking thousands of miles to recoup if there is any benefit. If there were such a wiz-bang, no-muss no-fuss technology, I figure it would be installed as standard equipment from the factory.