From the moment I started driving cars, I made it a sport to find ways to get as many kilometers/miles per tank of fuel. This page lists how far various cars got, and lists 10 tips to get similar results.

Year Car Result Comments
2013 Renault Megane III SW, 1.5 DCI
Megane 3
3.5 l/100km
29 km/l
68 MPG
Cold engine start
Over a stretch of 120 km / 70 miles of B roads
Start and end point at same elevation
2007 Renault Megane I Hatchback, 1.9 DCI
Megane 1
4.5 l/100km
22 km/l
53 MPG
Full tank emptied driving on B roads
2003 Peugeot 206, 1.9 D
Peugeot 206
5.5 l/100km
18 km/l
43 MPG
Full tank emptied driving on A & B roads

Needless to say, I am very much impressed with the latest developments! This performance was achieved using these behaviors:

1) Avoid using your breaks. Breaking transforms kinetic energy to heat and is wasted.
2) Keep distance. When the person in front of you slows down, release throttle only.
3) Look ahead. Anticipate traffic lights and release throttle or keep speed accordingly.
4) Limit speed. Air drag is quadratic with speed.
5) Shift gears up early, but not too early: below 1500 RPM in higher gears is too low.
6) Cruising at 1750 RPM works best for me. (Note that these are diesels. Not sure if this RPM applies to petrol cars.)
7) Use computer's current consumption as feedback to see if throttle is pressed too much.
8) Keep tyres at correct pressure.
9) Maintain car. Refresh oil at regular intervals.
10) Use air conditioning on warm days to keep sharp.

Of course, safety comes first always. Using these behaviors should not jeopardise others.