1)Getting a ecu remap is one way to gain more fuel consumption from your vehicle.Ecu tuning software remaps cost between £200-400 depending on what kind of car you have.What remapping does it give's you better power and torque,and increase more response to the foot pedal's acceleration.
2)Check your cars air filter system don't worry its easy to replace and check.Get to your bonnet a find your air filter firstly.Pull it out and hold it pointing to the sky possible and towards the sun.The way to tell is if you need a new filter is if you can't see sunlight coming through the end of the cone,then its dirty and you need a replacement.There not that expensive as you think,i suggest k&n or any other leading good brand will get the job done fine.
3)Stop overtaking and speeding,this is the most common cause that reduces your engine being efficient.If your car is auto transmission,don't boot the gas pedal,accelerate smoothly so the gearbox can shift up into the higher gears.If its manual then keep in the right gears and the right time.The more you overtake and speed,the more quicker your fuel will burn up.
4)If your car has a turbo then i suggest shifting before your turbo kicks in and boosts up.Turbo's yes take lots of fuel consumption away if you only let them.My tip is to shift into gear as soon, before the turbo produces psi boost,as most truck drivers starting to use this way.You can buy a gauge that shows you when your turbo produces boost.Or you can get a boost controller so you can be in charge of how much you want the turbo psi pressure to be.
5)Did you know that new alloy wheels and thicker tires, turn many heads and they make your car handle better on the road.If they are more wider than the tires that came from the factory or showroom then you will certainly loose mpg.My tip is to keep the old tires in a garage or shed,because when you want to sell your car you can keep your new alloys and put back on the stock wheels back were they belong.For motorway trips stock rims and tires give you a smoother ride plus you get extra fuel economy compared to the new rims that you just bought.
6)If you have a lot of trash in trunk,then that will reduce your fuel consumption.The more weight you car has the more power it needs to move which means more fuel will burn.So i suggest clear out your heavy junk,like golf clubs etc ...
7)Turn off your A/C,because air conditioners take massive amounts of fuel away from your car.Instead just open all the windows or your sunroof in your car,that way you save money and plus you will enjoy the breeze from the wind.If you still want to use it you can adjust the fan setting,usually found on the dashboard to the lowest,meaning it will take less amount fuel
8)Check you car tire pressure and make sure they not under inflated.Under inflated tires have more rolling distance,which bascailly means is that you cars engine needs to burn up more fuel eg diesel,petrol to keep your car moving.Go to you local petrol station you should find a tire pressure pump,with a built in gauge that tells the the psi in your tire.
9)If you want to travel local or the destination were you want to go is down the road,then leave you car were its parked.Your best of walking on foot because this way you save fuel,money and get some exercise that is good for your heath.
10)Change you car to a more fuel efficient vehicle or get you car converted to lpg.Liquefied petroleum gas is the cheapest around but the only downfall is you need at least £1000 to get your car to run autogas.If you are a taxi driver then switching to it can save you loads of cash.