For the "human" interview, none really - they don't try "trick" you. They just want to assess you honestly and see what you are like, which is nice. Obviously you need to be able to discuss and answer intelligently regarding whatever you say your skills and experience is. The computer based assessment tools ask weird questions and some interesting brain-teasers, but these are to test lateral thinking and things like that - more of a game, no "wrong" answers really.
