The best upgrade you can do to improve your car's fuel consumption, in my opinion, is to improve your driving style.
The best proof for this is using our 2001 Rav4 AWD I can eke out around 7km/L or so doing city driving, basically driving my wife and daughter to their respective destinations and picking them up. Someone else driving the exact same car gets a little over 6km/L going the exact same route.
It all comes down to driving style. I like to be gentle on the throttle and anticipate when I should let up on it and get ready to brake. I've seen other people apply gas, lift off, apply gas, lift off, lather, rinse, and repeat. I've also seen people brake for no apparent reason, which will require you to increase RPMs on your car to get back up to speed.
Getting up to speed and coasting is a lot better than constantly speeding up and slowing down. You just need to be conscious of your driving style and aware of what you need to do to improve it.
I've also become more defensive as a driver because the number of "kamote motorists" (or idiot motorists for lack of a better term) has steadily increased. I drive slower now and make sure I'm in the correct lane most of the time just so I don't have to contend with them. I also control my temper now and prefer to let people do their crazy overtakes while trying to minimize my own lane changes or overtakes. Patience is the key.
Out.
