haha, the crouching duck was weird!
its all been pretty much covered by rob, but heres a little more..
in the psych test, im 95% sure you wont like your tester, but keep your cool. in mine and from my other mates who've done it, they try to 'attack' you to see how composed you stay, just be cool, calm, and polite.
with the main interview, you really have to know your stuff. weapons, vehicles, installations, and your role. also know current events (hint: the 4 operations) and people (hint: DF leaders and also political figures)
and finally, dont lie! at all, they'll just keep asking and asking and you'll dig yourself in to a bigger hole
hope that helps, good luck
oh, and take a good book, you'll be waiting around for ages