This is from reading various forum posts, and hoping to summarize and get some confirmations.
1) Think through your complete trip: where do you want to use your limited "20 miles" of electric power and then turn on PURE for those times
2) When on freeway, switch to ECO mode and "HOLD CHARGE" to preserve your battery for future local driving.
3) On Freeway, turn off B mode as it will hurt mileage (also don't turn on "CHARGE" for anything but downhill)
4) On Freeway, going downhill, turn on "CHARGE" mode to gain some "free gravity" power and go back to HOLD at the bottom of the incline
5) On Freeway, if possible, drive at speed limit; going faster will consume more fuel, which is true for any car, electric or gas
6) Automated cruise control (and Pilot Assist) may negatively impact mileage, if you can be a better hyper-miler driver than the Volvo
7) And there are other items, such as minimizing use of car climate extremes (heated seats/steering wheel with coats are more efficient than running the car heater); keep windows closed, minimize weight; no jackrabbit starts, coasting in advance of a slow down, instead using gas to only then use the brake.