there are a ton of things that work
tuning the driver to drive smoothly , not following so close so you can adjust speed more evenly , braking properly driving slower , drafting at highway speed , tuning the engine to make the most efficient use of the fuel , clean air filters & less air restriction into the engine & cooler air , lower weight oil , new spark plugs caps rotors etc , properly gapped , hotter spark , better ignition wires , tuning the engine to make max power with the fuel used , proper jetting ,accerator pump & timing adjustments , tires inflated properly & tires with less weight or rolling resisance , make sure the brakes are not dragging , synthetic oils with less resistance to flow , lower the car , improve aerodynamic drag , optomise gearing , too low RPM may not incrase milage as the engine becomes inefficent sometimes , better cam designs , ported heads & intakes , bettter manifolds or headers , anything to help air flow in & out of the engine , clutch fans to reduce drag on the engine when not needed , wheel alginment , lighter wheels , newer style ing wires with less resistance for hotter spark @ the plugs
