Change all fluids (engine Oil, Brake oil, Gear oil, Coolant etc) whichever required.
Change all filters (oil filter, Air filter, cabin filter etc) whichever required.
Change spark plugs, use Iridium plugs (they last long almost 1 lac milage)
Do an engine flush before changing Engine Oil
Use Fuel System Cleaner once
Use Liqui Moly Ceratec Once
I hope doing all these measures, will definitely improve your car's fuel economy and ride quality.