I was averaging 31-32 MPG w/my HEV SX Prestige when I first started driving it last fall. Cold weather doesn't help! But what I discovered is that there is a 3-4K mile break-in period, which seems to mostly be for conditioning the battery. I would watch the hybrid diagram while driving on the highway and it would charge to just over 50% full and then discharge to just under 50% full, so not much use of the EV capability! A few months later, even in the dead of winter, it was charging to 75% full and discharging down to as low as 25%. My gas mileage improved to approx. 35 mpg and now in the warm weather, I'm getting closer to 38. But note: If you drive on the highway a lot, especially over 70 mph, you will be getting somewhere in the low 30's, even in warm weather. So have patience during the first few thousand miles, slow down on the highway, and learn to "feather" or "pulse" the gas pedal to keep it in EV mode longer, and you will get much better mileage. Holding the gas pedal constant starts the ICE more often.
One more tip is to try to keep the power display in the "Charging" zone for as long as possible when braking. This avoids using the actual brakes and is using regen battery charging to slow the car. If the needle is pinned at the bottom of the charging zone, you are braking. It's hard to tell when the actual brakes come on (which is a good thing!) To be most efficient when braking then, is to start using the pedal earlier and coast into the stop. Best practice is on the highway off ramps. It takes a while to get a feel for how much longer stopping distance you will need to achieve this.
Fantastic car. Love it!