Congrats, nightrunner! And welcome to the forum.
I just did my first fill on my new-to-me '07 Civic LX 1.8 5-speed, and saw 50 mpg US.
Start a fuel log: you will want to track your actual fuel pumped vs. distance traveled, since the onboard display is likely optimistic. It's ~10% high in my parents' 2010 Civic. My '07 doesn't have a factory gauge, but the ScanGauge also read 10% high before calibrating it.
As for mods, I did 15 mostly small ones that increased my Civic's highway efficiency by 15%:
http://ecomodder.com/forum/showthrea...7-a-30111.html