I don't rely on just one method, I use every resource I can get my hands on - here's a short list of the main ones:-
Face to face lessons at the CLL at Newcastle - by far the most valuable resource!
The Greek audio course at
Kypros.org - I stick 5 on a CD and play it continuously in the car. When everything sounds familiar, I move on to the next 5 - I'm onto lessons 40 - 45 at the mo.
VTrain vocabulary trainer - I reckon vocabulary is more important than grammar for communication - although obviously you need a bit of both.
Listening to as much Greek radio and TV on the internet as possible.
and of course:
Going to Greece as often as possible!
I think that's about it!