I just attended the assessment day in Sydney so I can pass on a little information which may be of help.
Logistics: First up, book your flights and accommodation as soon as you can. I flew up the day before so I would not have to worry about getting there on time. I stayed in a hotel about 10 minutes walk from the venue. The venue is only a one minute walk from North Sydney train station and this is only about 1/2 hour train trip from the airport. I had an 8.45 flight from Sydney to give myself plenty of time.
On the day, a young lady from the Gold Coast spent all day worrying if she would make her 6.30 flight. Finally she decided to leave early so she could make her flight. Unfortunately she missed one of the tests and will now have to wait a few months till she can do this test in Brisbane. If you get this stuff sorted now, less to worry about later.
As for the day itself, the Air Services guys were great and do their best to make the day more relaxing. You can't really prepare for the tests, all you can do is be well rested and ready for the day and just really be yourself. We don't know what they are looking for and there is no feedback given on the day.
I now have to sit back and patiently wait to hear back from them