Better fuel economy, change the spark plugs and ultrasonic cleaning for fuel injectors.
Spark plugs work in a very hostile environment. If the spark plugs have been used for more than 45000 km it is time to change them. A set of new spark plugs that are not covered by a carbon layer will surely improve the fuel consumption.
The only relatively safe method for cleaning the fuel injectors is to disassemble them and put them in an ultrasonic bath. The fuel injectors are loaded into a device and by using a combination of special detergents an ultrasonic vibrations the carbon is shaken off the injector. The cleaned injectors will deliver the optimal fuel to air mixture thus improving fuel consumption. If the injectors have been functioning for more than 90000 km you should consider a professional cleaning service. It will not be cheap but it will still be cheaper than buying a new set of injectors. Another method is to add a special solution for cleaning the deposits coating the injectors. Given the great variety in wich these solutons can be found, you should read the instructions carefuly (especially the dosage).