The initial rounds are more oriented towards psychometric and aptitude testing. Do some practice of basic maths problems (long division etc) and IQ testing type stuff like progressive matrices
Later rounds will include interviews and there it will be advantageous to have read as much as possible in the PPL line (as SRT suggested the FAA website has good basic flying info) just to show that you have a genuine interest. Too many applied in the past simply because it sounded like a good idea and not because they really want to fly aeroplanes.
Good luck.