I do Oz/NZ once or twice a year, and the jet lag approach you need tends to be different from transatlantic (which I used to do monthly).
Usually I find the best method is to try and sleep on both outbound flights and then make sure I'm out in daylight when I get there. if I'm feeling tired/hungover(!) I will grab just enough sleep in the morning to keep me awake and then ensure I'm out and about until a reasonable time in the evening.
For the usual return journey (i.e. landing early morning in the UK) I've found the best way of minimising jetlag on arrival is to stay up for the first sector and then spend transit time staggering around in small circles until I can sleep on the final sector. Then I'm more or less OK.
As others have said, the key is to convincing your body to follow the new time zone, which means mealtimes appropriate to your destination and getting out in the sunlight as much as possible. You can take melotonin too, but (a) it's not available without prescription in the UK (but is in many other countries) and (
it doesn't work for some people.
EC