I drive a 2005
MCS.
I was getting 30 mpg on three tank fulls, getting about 380 per tank.
I decided to try to see if I could get better mileage and started shifting sooner, keeping those revs around 2500-2800 at the shift. It took all the fun out of driving and my mpg got worse. I got 29 mpg. I said to heck with that, and went back to driving like I used to, shifting about 3200-3600 (when it "feels right"). I check my tire air pressure and make sure it is at 35 psi. I just drive reasonable and don't rive overly aggressive. I drive calm and enjoy myself and I'm now getting 32 mpg.
I use a program call Fuel Log on my hand-held (PDA) to keep track of my fill-ups and gas milage.