One thing that helped me a lot is pumping up the tires. The HCH tires come from the lot at around 30psi, so as to give a bit of a more cushy ride due to underinflated tires. the tires are rated to handle 50psi safely however, so if where you live has nice, well-maintained roads (no potholes or extended trips over gravel/unpaved roads) then you can get a big mileage benefit by pumping the tires up to 40-45psi. I actually prefer the higher pressure myself, the car feels a lot more responsive during turns and I have a better feel for the road. The ride is still plenty comfortable, I haven't received any complaints from passengers about it.

Another thing is with hills is that you will improve a lot with practice. The key is to watch the CHRG/ASST bars and feather the throttle so that you don't go into "forced charge" going uphill, also, anticipate stops and 'tap' on the brake lightly a long way back, just so much that you get almost full CHRG without applying the brake pads. You will get replenish the battery a lot more, whcih helps. Over familiar routes, you'll get a feeling for the subtleties of how to drive based on how much charge you have in the battery and mileage will improve. I've gotten good driving up and down the hill where I live, to the point where I can actually feel the electric boost/charge kick in, and respond accordingly even without looking.

I allow myself pick up speed when the incline is at a lower grade, and "coast" up the steeper grade portions. When cresting the hills, I apply the assist. I also allow myself to roll to a stop that's on an incline rather than slowing using the brake. Keeping a close to steady throttle level, with some "feathering" will be the most efficient.