I'd say your first steps would be making it more aerodynamic for sure. is this a picture of the car you are referring to?
If this is it, it surely has potential to get good economy especially if fitted with a standard tranny with long legs. Is is rear wheel drive? Looks like it would be.
It looks low to the ground and somewhat streamlined to begin with. Have you read about
basjoos's civic? It's a must read for someone wanting to get serious fuel economy.