Good advice for any car is to drive it fairly gently for the 1st 1000 miles. In fact, more or less everything is well-served by approaching it gently for a little while at first.

You should see a large increase in MPG after 1500-1800 miles, to the tune of 2ish mpg, and another 1mpg or so around 3000 miles. Maybe another after the 1st oil change after that, but that may be lost in the tank-to-tank variability.

Another issue is that you are getting used to the nuances of the HAH at the same time, so its hard to separate what improvement is form you the driver, and what is from the car breaking in.