i hear a moped swap is good for some ridiculously high mileage numbers...
I'm a firm believe in "it's not what you drive, but how you drive".
Like Ravo said, upkeep of the machine is important to MPGs as well.
I've also read that coasting to a stop in gear will help as opposed to coasting to a stop in neutral.
that doesn't logically make sense... in gear, the engine will be slowing the vehicle down (similar to downshifting) and will be turning faster, thus using more gas... UNLESS you are in an auto, and the speed you are at is below idle speed in what ever gear you are at, and the speed is decreasing still, and slowing the idle, almost stalling it, but the idle is pushing the vehicle forward, as to slow the rate of speed loss, but a) this is virtually impossible, as gear selection in the transmission is partially relative to the speed the vehicle is going, ie, it will go from 4th to 3rd, before the motor reaches idle speed
you will coast farther in neutral than you will in drive (not counting the fact that an auto idling in drive will never fully stop, unless on an incline or on the brakes)
your best bet would be to just drive like a granny... if you have a manual, then coast in neutral, rather than downshifting, i would NOT recommend that in an auto, as it wears the trans out being shifted constantly...
additionally, use your brakes as little as possible, every mph you lose by using your brakes is a mph you had to gain with the gas pedal at some point... if you can coast to a stop at redlights, using minimal brake pedal, then you will have used less gas to get to/maintain that speed over distance, AND you will have to replace your brakes less often... win/win situation, but it WILL take more time to travel the same distance...