Agree with Mike.
Ignore the instant mileage and dash calculated mileage.
"Best to use to old method to verify your actual mpg. Fill up - reset one of the trip meters - drive 'til it's close to empty - refill - divide miles driven as indicated by value on trip meter by gallons added during refueling."
Its going to vary with car warm up time (if you live in the cold), if you live on highways like ours (290, I10, I45)...
The only other things that I would add are:
- a semi-regular fuel injector cleaner to a tank every time you change oil.
- tire pressure (keep mine at 35)
I did notice that my mileage was going down, but my threw a CEL code for the crank shaft position sensor.
Replaced that, at the pep to the motor and mileage came back to life.
Mine is a '12 with 80K