I've done one in Brazil and there is nothing really to revise for.
Three parts...
Part One
Short interview : Only thing is to be honest.
Part Two
Multiple Choice Questions : Lots of Mensa like, "Which is the odd one out?", "Which of these is the next one in the sequence?" type questions, using strange geometric shapes.
Part Three
Hand/Eye Coordination Tests : A series of test cards, where you have a pencil in one or other hand, and sometimes both hands, and have to follow either a line on the card, or start copying a pattern repeatedly. You'll do the first few seconds able to see the card, then your view of the card will be blocked.
That's it, can take up to about 2 hours.