After servicing MAF sensor, 7 km/l is really good. However it can be further improved which will be marvellous for a Surf. Good contact cleaners are 7CF Contact Cleaner and PERFECTS Contact Cleaner.
Get the following services done:
Clean the fuel injectors
Clean the fuel filter
PCV valve service
Throttle body cleaning
TPS sensor cleaning
AFR sensor cleaning
Ceratec treatment for engine oil
Catalytic Convertor unclogging (depending on condition)
Decarbonisation of engine interior
Each of these services required different kinds of materials and techniques. These services will add add an expense of maximum 5000 Rs an year but they will keep your car maintained like brand new and increase engine life. They will increase fuel mileage drastically. If you need further guidance about procedures, let me know.
Besides above mentioned services, do the following as regular maintenance.
Always use genuine air filter, oil filter from Toyota 3S dealerships.
Use engine oil Shell Ultra 5W30 API SN GF-5.
Check the Plugs and Coils regularly. Don't service plugs, change them.
Use Caltex red coolant. Coolant capacity is 8.2 litres (4.1 litre coolant + 4.1 litres saturated with distilled water) for 3RZ-FE 4WD Automatic. (Let me know for the correct procedure)