Improve mileage for my new used 2003 civic
 

Hi I am the very proud owner if a new used 2003 civic hybrid manual transmission with 121k miles. IMA was replaced at 92k. Car is really fun to drive. Needs new tires.
SO
Former owner said he was getting 45-50 mpg. The dash is telling me my first 110 miles on my first full tank is averaging 34mpg. (I intend to calculate it myself at next fill, but is it your experience that the car's mpg average estimate is off?)

Another thing that's unexpected: the average seems to improve when I add on more freeway miles (of which I have drive very few) and decreases again with more city travel.

I understand that replacing the tires will help some, but was the seller lying to me? Or is it something about the way I'm driving it?

And what are your opinions of shifting when the dash recommends in terms of optimizing mileage?

THANKS!