Just filled my Wagon this morning: 803 miles, 15.8 gallons = 50.8 MPG. This tank was some commuting (30 miles round trip, 80% highway, some traffic, usually at 80 MPH otherwise); and a round trip to NYC. NYC trip is about 475 miles, some traffic, 75-80 MPH most of the time, but this trip I had an extended run at 90+ MPH because that's how fast the traffic was moving. I expected to take an FE hit because of that, but not so. A/C on for most of the tank: It's been hot and humid here.
I'm sharing this because a properly set up TDI can deliver really good FE without any special driving techniques. I use the cruise and A/C when I want, accelerate hard occasionally, don't hesitate to rev the engine to 3500-4000 RPM occasionally. I do have 15" wheels with stock tires, and a .700 5th gear which drops highway RPMs by 150-200, depending on speed. 75 MPH is 2400 RPM, for example. I think this helps quite a bit. I also have some PD150 breathing mods and a downpipe without a CAT which might help, although my Golf with a stock exhaust delivers similar FE.
Make sure your car is in top condition (injector condition, correctly set mechanical timing, clean intake, vacuum system working properly, turbo boosting correctly, and so on. And keep in mind that it appears that some cars simply deliver better FE than others. Not sure why, but I've experienced this with the TDIs I've owned over the years.