Though it's Aussie, the 'RAAF Flight Screening Program' thread may give you some useful info about preparation for boards and so on.
Honesty, enthusiasm and determination will be his most useful attributes, though of course aptitude (which you can't do a lot about), medical suitability (ditto, beyond a certain point), school marks and serious prior attempts to study up about the job he's proposing to get will also naturally be factors.
Best of luck.