There are fuel additives out there, I haven`t tried this so don`t know how effective it is -
Envirox? Fuel Saving Additive ? Energenics Europe Ltd ? Envirox ? The Fuel Saving Additive on the few occasions I`ve checked the fuel economy on my Corsa (no trip computer so have to do it the old fashioned way) I get around 65mpg.
You can also get your ECU remapped which is also supposed to give more power and better economy.