cheap/easy mpg boosters?

so my 70 dart currently has a 225 /6 in it. i intend on swappin in a 360/904 down thge road, but that wont be for quite some time..so i was curious if anyone knows of any ways to improve mileage? i do want to put on dual exhaust, by splitting the single pipe into a Y but thats all i have planned really.