Practice essay writing, Maths problems and familiarise some words from the dictionary :3.
It's also about luck, my neighbour guessed 3/4 of the multiple choice and they got in :S
I agree with SmRandmAzn, i reckon they choose people from those types of school because i compared mine from my neighbours and It was close(infact my maths and written response was higher than his) and he still got accepted.
I didn't try for the year 10 one because if you think about it, i have to wake up around 5 or 6am everyday and i can just imagine te amount of homework they get. In the end, all I need is a decent score to get in my uni course which I can achieve through strategy, hardwork and my current school.