Lets get one thing straight- by coasting (putting the clutch down and rolling) the engine is using the same amount of fuel as idling which is high MPG but isn't the best. By engine braking (using your gears to deaccelerate slowly) you are effectively using zero fuel- at least in most modern cars.
Obviously you could argue that the most fuel effective way to drive is to actually turn the engine off when going down slopes. PLEASE DON'T DO THIS. The reason being (my little anecdote)- I was in a car once my friend turned his engine off at the top of the slope. Stupidly not realising that the breaks are dependant on the pressure which is maintained by an engine running. Needless to say when we needed to brake properly we couldn't- luckily we realised before it was too late and switched it back on.
There are many factors which you can consider to save fuel:
- Keep tire pressure high - by doing this you are creating less resistance on the road.
- Remove unnecessary objects like roof racks which would effect the aerodynamics increasing resistance of the vehicle.
- Unnecessary luggage/weight in general.
- Use higher gears as much as possible.
- Windows as cooling are better at saving money than using A/C at speeds under 50mph if my memory serves me correctly.
- Only fuel up half a tank - by doing this you could save yourself a lot because the weight of half a tank of fuel unnecessarily being carried around especially when you do the same route every day and can easily predict the best times to refuel.
- Use www.petrolprices.com (UK) to check for local
prices if your wanting to save money.
- I met someone who once said that they only fuel up at night because at night it's colder and fuel expands therefore they get more from the pump. I'm not sure how the pump system actually works but I thought it was an interesting point.
AA tip website: http://www.theaa.com/motoring_advice/fuels-and-environment/drive-smart.html