Expect it to be quite a fun atmosphere it was last time! and nothing to be nervous about really!!
Get onto the BBC Bitesize Maths and Physics websites and brush up on Trig, DST, bearings, SUVAT formulas etc etc...
There is a link in a post above to some other OAT selection revies.
Also try googling Pilapt and Compass as they are the Tests OAT use...(I think!)..
..Hope that helps...has anyone got there dates through yet?