Hello all,
ATCO nearly 30 years in (LHR,LGW,TC). With regard to preparation prior to starting at the college I would be in agreement with the comment above.It isn't worth second guessing the actual course content and the risk is what you find out may be different or at worse at odds with what is taught;...however,reading aviation mags (Flight etc.) ,swotting up a bit on aircraft types/performance/configuration and a bit of general background on UK ATC would be very useful if only for the feeling of preparedness it may give.Having said that I wouldn't bust a gut and burn the midnight oil committing a load of stuff to memory.
Hope that's of use,good luck.