Pay attention to your instant fuel consumption display, the bar graph under the odometer, that will really help you learn what efficient driving is (best pedal position, best speed, etc.). If the graph isn't there you can turn it on, there are direction in the owners manual if you have one, I don't remember how to do it off the top of my head.
If you're speeding, or in bumper to bumper traffic on the highway that will hurt your mileage. Using the AC also takes a hit. The amount of assist you mention sounds normal to me, you'll only see assist when accelerating.
Keeping working at it, good luck!