With the economy the way it is, and the current price of petrol and diesel being so high, having a vehicle which doesn’t cost much to run is increasingly important. The primary cost associated with vehicles is fuel (unless you don’t use it very much – in which case it would be insurance), so anything which can help to reduce the cost of getting from a to b would be appreciated by most drivers.
This isn’t really as easy as you might expect, but there are some small things which you can do which will have an immediate impact. You can, for instance, change your tyres to a different model which offers greater fuel efficiency or change your fuel to a more efficient variety. Both of these will have an effect, but it will likely be negligible.
To gain far greater fuel efficiency, you would need to do a large overhaul of the vehicle, replacing parts, getting rid of others, all with the aim of reducing the weight of the vehicle.