Most of the above information is correct. To achieve maximum fuel efficiency, all of the above will work. But for realistic high fuel efficiency - IE, not coasting to a stop from 60mph on the freeway - things require a different touch.
For instance, the highest gear is not always the best. If you are at 35mph and in 5th gear (Around 1800RPM in the average car), you will actually be wasting more gas than if you were in 4th or even 3rd. Ever car has a certain range where it gets the best fuel economy, and it is usually right before the secondary air system opens up (on newer FI secondary intake runnersor carburated secondary "power" venturis cars with more than one barrel). Most cars have secondaries that open around 2800-3500 RPM, and this lets more air, and thus, fuel into the engine. The best RPM to be at to achieve best fuel economy is at right below this point.