Hi Eager,
I've just been selected by OASC after a couple of attempts at the selection process. Here's just a few things that may help that are off the top of my head. Firstly do your home work! don't mean to sound patronising but get on the BBC news 24 web page and learn inside and out 6 topics both international and domestic, so that you can name names and form your own opinion. When asked a "when" question always answer with a month and year. Practice your basic mental arithmatic untill your quite quick, even the very basics. Show the interview board that you have a sense of adventure, that you are independant, perhaps some charity work, and a genuine interest in the forces. Have an idea of the down sides of military life not just the rosey side. If you get through to part two, thats the hangar tests, then keep calm in all the tasks, be yourself and enjoy, the tests are quite a good laugh, try not to work against your team, team work is a big tick. Finally make sure you are reasonablly fit, you carry out a bleep test.
Sorry if all that was a bit mixed up but if you want any more help email me. finally good luck