Improve mpg when using cruise control?

I just installed CC yesterday and on the way in to work I was getting about 8 mpg better than normal using the CC.

 

Don't get too excited about that.
While it might be true, basing ANY conclusions on what the displayed fuel consumption number is is not a wise thing to do.
It often will lead you astray.

 

I drive 152 miles round trip daily including through a 6% mountain pass. I notice my MPG reading does reflect the uphill vs. downhill (closer to 60 going down closer to 50 going up). I can hit 4K going up the hill with CC on and zero throttle going down with some regen braking filling the battery. Approximately 3000 feet elevation change. Regardless, I'm using half the fuel I used to with my Accord. w00t! The car is going to pay for itself.
I also notice the cruise control keeps the green bar just under the red power zone better than I.