I would recomend learning how to conserve as much gas as possible before learning to rely on electric mode. During warmup period, i try to make my engine work all te time. I won't let the car use electric. this makes my starting mpg around 40.. which, my overall mileage currently is 45. Still waiting for the break in period to stop. (my neighbor has 20k on his car and still gets low mileage)
I've been watching the hybrid system work on the screen. I've figured out two "good" ways to drive.
One: try to keep the gas engine running. At al times, i try to have the generator give back to the battery. Once the battery gets fuller, the motor will assist and your mpg will skyrocket. I mainly use this technique around the city (45mph average.. most do 50 if not faster) So, i guess you could call this faster/highway driving. At times, i've been able to achieve 75mpg on my 5 minute graph. Best would be 65+ for 20 minutes.. till i jumped on highway.
Two: Try to cruise in electric mode Half the time. If you cruise in electric mode all the time, you'll eventualy start waisting gas when your battery runs down to half way. Your engine will work harder to make electricity.. your electric motor will work harder to keep you up to speed. So, alternate. Watch very far ahead of you to see when other cars are slowing down. You may feel strange.. but try to very lightly brake from a longer distance. This uses the regenerative breaking a little more and charges the battery a lot faster.
Using both of these techniques, i don't experiance warm up "bad mpg" and they make up for me having a lead foot. at times i speed a lot, but still manage to get 45mpg. If i didn't speed, i would be achieving somewhere around the epa 60mpg. Maybe one of these days i won't speed. probably not though.