gas mileage

well im about to replace my oxygen sensor because my van is getting horrible gas mileage.
I mean its using half a gallon to reach um, not even operating temperature like just the point where it is warming up. i cant calculate this is mileage because its not even going anywhere im getting like a few miles a gallon its atrocious

ok and these are the new parts i put in
plugs
wires
cap
rotor
air filter
pcv valve
fuel filter
new drivers side fuel injector


well lets assume the oxygen sensor cures my problem.... what else can i do to improve gas mileage on my beast?

Tire pressure correct, light foot on the accelerator, use synthetic lubricants throughout.