anything you do to make the car more economical will cost more unless you're keeping the car for a VERY long time.
things you can do (in no particular order)
1. warm up the engine prior to driving (tho i'm not sure if the petrol lost by having it idling would cancel out)
2. only use the air con over 40mph (mythbusters did a test which showed that this seemed to be the point where it was more economical than the added drag from a lowered window)
3. economy tyres
4. blue motion aero underbody panels
5. remap
6. use V-Power/Momentum (though from my calculations the added cost is negated by the improved fuel economy)
7. do an IAM (or similar) course. it really improves your forward vision and makes a smoother (and hence more economical) driver
8. try and plan trips so you're doing several things at once in the most efficient fashion
the 2.0T is an impressive engine. when it was new, it was very economical considering the power that was available. just as a measure, i swapped from a 2005 1.6MPI to a 2006 2.0T and saw a 10% drop in fuel economy for a 95% boost in power. on long trips the K03 engines will see up to 40mpg (the K04s are a little more than this iirc because they're off boost for longer on long trips) but around town they really aren't that good and there's just not much you can do about it!