Tbh, theres not much you can do, I drive fairly economically out of habit, and weight, heavier right foot, even driving at 80 over 70 or 60 doesn't make any difference. Its all about the roads you drive ime. I was getting far better mpg doing longer drives than now I've moved and everything is 10 minutes away. You'll probably find you get better mpg doing the longer drives regardless of how you drive! 
Nice and cheap if you run veg too, just be prepared to change the filter every day and every rubber seal failing. 
Nice and cheap if you run veg too, just be prepared to change the filter every day and every rubber seal failing.