Since there are some complaints, I thought a thread summing up standard and non standard advice might help. There are a lot of variables, many of which are not even CRD specific. The Faq's should be reviewed, but there are new things to add. I'll start the ball rolling, others chime in. I imagine when all is said and done, many of the whiners can get some improvement...even those that work for Consumer Reports:
1) Tire Pressure: supposed to be 33psi on the stocks. But are you really good about measuring the pressure on a cool morning before the sun hits the tiresand you have driven anywhere? Might be surprised at how low yours is! Worth 5% by common lore.
2) Drive the speed limit/2000rpms, use cruise: This was gone over at length, but there is a sharp drop off above 55-65mph (just below 2000rpms) To many tech reasons to list, but don't whine about mileage if you are a speed-demon.
3) Clean the MAP sensor: Don't believe it? Well, it only takes ten minutes, and can't hurt.
4) Change the air filter: Might be nasty in there! Check out the new after-market one.
5) Think about the ORM: hey, try it, you'll like it.
6) Check your Odometer against GPS (or other real data). probably off by as much a 10%
7) Be honest about your driving style: You probably aren't as gentle as you think.

Maybe knock off that muffler: your risk is your gain. It will probably still pass inspection.....
9) Where do you get your fuel: This matters the most. Truck stops are usually better.
I'm a alt-fuel kind of guy, but more important is saving money and using less!!