Reply #2: Not necessarily driving slower, but...

[HamstersFromHell]

...driving at the engine rpm that is it's torque peak. That's the "spot on the tach" where you engine is at it's most efficient. Of course, this only applies to vehicles that are reasonably aerodynamic to begin with. :)

Of course, all the other tricks apply...

Don't use your a/c. Same applies to defrost on GM cars, as it briefly runs the a/c compressor.

Keep windows rolled up - in many cars the aerodynamic drag of a window down hurts mileage more than running the a/c does.

On pickups, if you don't have a camper shell or tonneau cover, opening the tailgate or removing it in favor of a cargo net will greatly reduce aero drag from that big empty "box" you're hauling around.

Inflate tires to the high side of recommended pressures. Most cars on the road nowdays run on underinflated tires through negligence of their owners. Not only does it cause premature wear to the tires and an increased chance of major tire failure due to heat buildup (see Ford Explorer), but it hurts mileage as it increases rolling resistance. Most any car can get a bit more mileage by running tires in the 32-36psi range instead of the "nice riding" 26-30psi recommended. Ride will be a bit rougher, but you may actually like the way the vehicle feels as it'll also be more responsive to steering input.

Use the lightest grade of motor oil your vehicle manual recommends. If you can use a 10w-30 instead of a 10w-40 or 20w-50, do so. It decreases internal engine drag by lightening the viscosity of the oil when the engine is warm.

Accelerate smoothly and brake smoothly, of course.

Do not let your vehicle sit to warm it up. Get in, start it up and let it run 30 seconds to get oil circulating, then start driving. I Hold engine rpms down less than 1/3 of redline until the water is up to temp., then use no more than 2/3 of redline for another 10 minutes until the oil is fully warm before ever using the redline or anything near full throttle. Note that this isn't so much saving fuel as saving wear on the engine. The quick warm up will save gas over letting it sit till it's fully warmed up, as with no load, the engine warms up very slowly.

Hope this helps!