1} Reduce car weight by throwing away your spare tyre. Get a can of "tyre-inflator" instead to repair punctured tyres on the spot. You can also join AAM or a similar organisation to get auto assist.
2} Reduce car weight by replacing all your car seats with racing car seats which are much lighter than those that came with the car. If you are driving a 7-seater and never use the last two back seats, well, throw them out.
3} Throw away your car boom box. Listen to slower, softer music. Fast music encourages gung-ho acceleration and driving as well as unnecessary car revving which burns more fuel for no useful reason.
4} Reduce drag by throwing away your car body kit and spoiler. Unless the body kit has been tested to reduce drag *specifically for your car model*, you can safely assume installing body kits and spoilers increase (not decrease) drag; hence increase FC. This is especially true for generic body kits/spoilers -- one size fits all cars type.
5} Reduce drag by throwing away your side mirrors. These things poke out too much, causing drag.
6} Throw away your air-con. Air-con = more fuel. Install fan, like in the good, old days.
7} Throw away your automatic gear box. Convert car to a manual car, as all real men drive. Automatic = more fuel.
8} Learn to use the car brake less. Try coasting instead. Instead of using the brakes, release foot off pedal, disengage gear, and slowly coast to a gentle, low FC stop.
9} Modify your car rear to reduce drag such as:

10} Reduce drag by throwing away your wipers. Make the air flow around car smoother with less abrupt change in flow. Use Rain-X instead.
I am open to more extreme measures!
Chris