I just want to parrot what Harp just said, plus add that you can't always compare your mileage to the mileage of others. Your driving conditions (i.e., hills, weather, congestion) are unique to you, so results will vary.
But like Harpo said, the guage will be a good investment. It will be your coach. Also, I personally would drive slower, which will easily increase your FE.
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