Traffic allowing, I tend to do the following:
Shave a few MPH off going uphill then regain it.
Coast when possible.
Follow other vehicles with 2-3 car-lengths in between on the highway. Pickup trucks or SUVs are easier to draft as they don't create air ripples. That is, IF I can find someone else on the road doing the same speed as I am.
Unlike cruise control, which tends to overshoot the set speed when cresting a hill, I can pre-emptively back off the power as I crest and not overshoot my preferred speed. On the one route I take to work, I've gotten so good with throttle control that through hills and turns, I can keep the speedometer right on 48 MPH, outperforming the cruise control in a BMW i3 (only EV I've driven the same route with that had CC).
The worst I've experienced is a Ford Escape on a hilly main road. Don't even attempt it. However, my work's 2011 Ford Focus does pretty good. With the PZEV, going downhill with the cruise on will shut the fuel off and use vehicle momentum to keep the engine spinning (the resulting holdback shows just how much energy it takes for an ICE to simply spin). I drove it for a week, all highway at 65 MPH, 80 miles a day. When I started, the dash said 28 MPG (80,000 miles on the odometer but I don't know when the MPG was last reset), and when I parked it, it was at 35.5 MPG and still climbing.
