Best thing one can do to increase fuel mileage is to change driving habits. Try driving a bit like "grandpa" around town, take off gently from stop lights/signs, build your speed slowly (it will likely PO the folks behind you too), but I bet you'll see an increase. Game I sometimes play is to try and not let the economy meter go more than halfway through it's stoke.
When on the highway, ease up to cruising speed. When using the cruise control, ease it back up to the set speed before re-engaging. I just did a 1K trip in the 560, averaged 18.5 mpg with my last tank at 20.21 mpg.
On top of that I also use Red Lines fuel treatment. I started using that in the 4.5 and have gained about a 10% increase in mileage. Granted, that's only about 1.2 mpg, but on the 4.5 that is significant.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.