Formally there is no real requirement to revise any of the material, it should be covered in the lectures if you are learning full-time, or in the notes if you are distance learning. You are right, though, that your life will be easier if you are pre-prepared. I teach general navigation and electrics, so this list will be biased towards those areas, but what I suggest you look at is the following:
Maths (little above GCSE level):
Trigonometry
Formula rearrangement
Vectors
Circular geometry
Physics
Newtonian mechanics
Circular motion
Wave mechanics
Electrics / electronics
Fourrier analysis (I'm kidding with this one - this is degree-level and is not required, but it would help!)
Gas laws