You simply need to learn how to drive. Every car I have owned has gotten better than the MFR listed average. Jackrabbit starts, excessive speed, and constant delta-V change (slow, fast, slow fast, goddammit get outta the way asshole, VERY fast, brake hard, slow. fast) will destroy your fuel economy.
get to the right and set your cruise control for the speed limit, or even lower. unless you are driving hundreds of miles, you will arrive within seconds of the guy that drives like you do, and use half the gas doing it.
I proved this to my leadfoot wife. For a couple of weeks, we took two cars everywhere. She drove her way, I drove mine. We each had a kid to keep it honest. Every single time i pulled in right behind her.
without fail. you gain nothing whatsoever from driving like that, except an empty wallet and some ulcers.