I had mine 2 weeks ago, still waiting for the results. My best advice would be to make yourself familiar with the basics of ATC etc etc, which you probably already know. And most of all prepare yourself for the personnel interview, you get 60 questions all in a similar vain to the psychometric questionnaire we filled in on the initial selection day, but this time you require reasons and examples for your answers, after this you then have a normal personnel interview aswell.
Best of luck.