K&N filters have a small flow advantage when new, but as they accumulate dirt they start to restrict more then a paper filter. So keep it clean,
If there is any basic maintenance that you haven't done, do it, but don't go replacing things that are still good. It'* easy to spend a lot more then you will ever get back in gas mileage. Fuel filter, PCV, oil change, air filter, spark plugs, wires, ect. You may want to try cleaning your MAF and IAC.
And the biggest thing of course is to get off the gas. Avoid heavy accelerating or braking. Avoid left turns, extra stops, ect.