Here's what I do when I want to drive economically

1: Shift at 2250-2500rpm.

2: Choose a route that minimizes left turns (or right turns if your country drives on the left side of the road)--there's more waiting turning left than there is turning right.

3: Consolidate errands (do multiple tasks in 1 trip), and make your first stop the FURTHEST from home--then work your way home--this will minimize cold starts.

4: Don't let the car idle to warm up. It takes longer to warm up this way AND you spend more time getting 0 miles per gallon.

5: If the car is at operating temperature, kill the ignition at long waits (I actually stop the engine in the drive through line at fast food places when the line is moving slow).

6: Drive slower. Fuel consumption increases as the square of velocity. At a point where aerodynamics becomes more significant than drivetrain friction (about 50-60mph), a doubling of speed cuts your fuel economy by 75%. Horsepower production rises as the cube of speed (it takes 8 times as much horsepower and uses 4 times as much fuel to go 100mph as it does to go 50mph).

7: For highway driving, use the A/C. An A/C compressor doesn't use more than about 1-2HP and will only have a couple mpg impact on fuel economy on the highway. The aerodynamic efficiency hit from open windows is far worse.

8: Use your basic engine bolt ons (Intake system, Header, Exhaust system). These are designed to give you more performance, but they do so by reducing pumping losses. As long as you drive conservatively, they will also increase your fuel economy.

Might I add that point 6 is the single most important one. NOTHING WHATSOEVER will influence your fuel economy more than your driving habits. Driving slow and accelerating slowly will make the single biggest change.

Contrary to popular belief, revving high doesn't have a huge impact on your fuel economy--you only take a very slight hit. I know someone who swapped out his 5th gear with a taller 5th gear that dropped his highway revs by 20% (3000rpm became 2500rpm at the same speed) and his economy went from 34 to 35mpg.
Why is this true? Very simple conservation of angular momentum. At *ANY* angular velocity (5000rpm vs 1500rpm, whatever), the ONLY thing your engine has to overcome to stay at that speed is friction. For highway driving (ie, when cruise is set and your speed isn't changing) an underdrive pulley will NOT have any effect on your fuel economy--neither will a lighter flywheel, nor will lighter wheels or any other rotating mass. These things only help with city mileage (where angular acceleration becomes a concern. Yes, internal friction does increase as the rpms go up, but so does engine efficiency in terms of converting chemical bond energy into kinetic energy (the Brake Specific Fuel Consumption is at its minimum near the power peak).