get high mpg

photo of my dashboard display taken with a macro setting

50% of a car's energy is used pushing it through the air.

aerodynamic - designed to slice through the wind rather than push ackwardly against it
lightweight - Honda Fit weighs less than 2540 lbs compared to a Ford Expedition at 5515 lbs. Heh, if there's only 1 person in the car . . .
engine tuning - add a good air filter to let the engine breathe
cruise control - keep it at 60-69 mph on the highway, and never, ever brake

Honda Fit is a ULEV - an ultra low emission vehicle