I also sat Gen Nav and Met. You definitely need to know the subject for those 2
nope! learn the methodology for gen nav and learn the database for met. I sat mine 2 years ago all q's were from bristol. I have a friend who has just sat his mod 1 for bristol and he said that 95% of the q's he had already seen and the rest was stuff he could work out from doing the QB (never opened the manuals).
My advice is that anything with calculations in learn how to do them as numbers can be changed, the 'wordy' bs learn and read the additional info that comes with some of the q's.
sod learning and when it comes to the interview jest get a tech interview questions book and wallahh....