Drive at an appropriate speed
Driving above the speed limit is illegal, but also means you use more fuel, and emit more CO2. Staying within the 70mph speed limit on motorways can bring savings of around 10% for your fuel bill compared to driving at 80mph.
Speed up and slow down smoothly
Every time you stop then start again in a traffic queue, the engine uses more fuel and therefore produces more CO2. Keep an eye on the traffic ahead and slow down early by gently lifting your foot off the accelerator while keeping the car in gear.
Change gears at lower revs
Revving does not help to warm up a modern car engine or improve its performance. In fact, over revving simply wastes fuel and increases engine wear. Using your gears wisely by changing up a little earlier can reduce revs, and so reduce fuel usage. If you drive a diesel car, try changing up a gear when the rev counter reaches 2000rpm. For a petrol car, change up at 2500rpm.
Avoid leaving your engine running
When the engine is idling you're wasting fuel and adding to CO2 emissions. If you're likely to be at a standstill for more than three minutes, simply switch off the engine.
Don't use air conditioning unless you really need it
Using your air conditioning can increase your fuel consumption so keep usage to a minimum to save on fuel and CO2 emissions. At speeds above 50-60mph it is generally more efficient to keep windows closed, even if this means using the aircon, as open windows will increase drag.
Driving efficiency tips courtesy of : ActOnCO2