I don't think I really qualify. I did get a few 60mpgUS tanks in the Passat when I was doing engine-off P&G, but I don't use that technique any more (it destroyed my clutch). Excluding that technique, I'd say that 56-58mpg or so was the best I could get back-to-back. Click on the green cleanMPG sig for more details.
I've been around 59-60mpgUS routinely in my A2 TDi 1.4, but that's an aluminium car with 3 cylinders (basically 3/4 of the 1.9TDi engine).
Basically:
Make sure you live somewhere with gently rolling hills so you can do P&G (but no big hills)
Temperate climate, 20 centigrade or more, but not in the 30s. Not less than 15c.
Never ever use your heater or climate control
Never drive in the rain
Never drive when there is a headwind
Never drive in the dark
Turn off all unnecessary electrical loads
Turn off your CD / radio, and LISTEN to your engine
Never put on a roof rack etc
Never drive less than 20 miles (and 30+ is better)
Never drive more than 60mph, preferably not over 55
Never drive in the city (stop/go)
Never drive in bad traffic (traffic jams)
Leave lots of space between you and the driver in front
Park facing down a hill (never start up a hill)
Park face-out (so you don't need to manoeuvre when your engine is cold)
Never drive an automatic
Never have passengers, empty out all unnecessary weight
Pump up tyres hard (40psi, or more)
Use LRR tyres
OK, some of the above is impractical if you live in a city etc. But a bad traffic day, or bad weather, will ruin a 60mpg tank. If you drive short distances, in the city, or too fast, you will never get a good tank. The 60mpg tanks I had were all in near-perfect conditions. I have no patience for the endless stream of people who complain about their MPG, when it turns out they drive at 80+mph.
Measure tanks brim to brim. Take a note of the miles at the 3/4, 1/2, 1/4, and reserve points. Use a trip computer which shows both instantaneous MPG and trip MPG, and compare your progress every day. After a while you will be able to tell the wind speed and direction simply by your MPG at particular points in your journey.
The car & mods don't matter as much as people think, as long as a) it's got a TDi, b) it doesn't have a DPF, c) it's manual, and finally d) it's aerodynamic (i.e., not the beetle, sorry guys). Mods will give you a few % extra, but changing the driver's right foot makes vastly more difference.