Ben I can't give specifics about your process, but here are some points about selection boards in general.
First of all be yourself; don't bung on an act, no matter how good you were in year 9 drama classes. They're trying to get a measure of the real you.
There will be a mixture of written work, speaking in front of an audience, team exercises, sample PFA (ie pushups, situps & beep test), interview with the board itself, and informal chitchat. You're being watched.
Don't worry too much about this process. The best advice is to relax a little (don't be lazy and goof around, I mean don't worry yourself silly and get nervous). If you aren't into current affairs (real current affairs - not tabloid 6:30pm television shows) then do some reading - SMH, Age, Australian ... The Economist ... etc.
The final tip is not to treat this as a contest between you and the other candidates. Quite to the contrary - teamwork and support is vital.
Good luck.