This won't apply to R18 owners
haha
1. (For R18 only) Always stay in i-vtec (1000-3000)rpm
2. drive smoothly
3. The best gas saver is your right foot so learn to control it
4. Turning AC off will improve gas mileage by 10-20% but bringing the windows down at speeds of 40mph+ brings consumption up again by 10-20%
5. Avoid maxing out the fan and temp controls. since the colder the setting, the more the AC compressor has to turn on. It's best to leave the temp somewhere in the middle
6. Make sure your car is well MAINTAINED. This could also lead to high consumption. Change oil regularly as well as the other fluids and parts to be replaced periodically.
7. Leave towards your destination a few minutes earlier to avoid hurrying, hence saving gas
Optional:
8. Since you've been so busy feathering the throttle and saving gas, just before your next gas fill-up, do an "Italian Tune-up", meaning, floor the darn thing to clear the engine from carbon deposit buildup.
Do this once in a while to keep things clean. It's like coughing out phlegm that's built up inside! haha!
these tips are more of a practical type than mechanical, and focus more on our attitude towards driving. Hope this helps!