Firstly congratulations on the job offer .
Secondly , there isn't much I would advise to do to prepare for the course , if you are not already I would make sure that I was comfortable using the phonetic alphabet as youll be using it everyday during training and in your career as a signaller . Other than that everything is taught in the order and way that it is for a reason , and trying to get ahead might mean you learn some of the fundamental stuff incorrectly or have misunderstandings . Some on my course did learn the bell codes as well although quickly forgot a lot of them once the course got started until they come to study the regulation concerned .
As for when you are on the course , you will only get out what you put in , personally i dont think it is possible to pass the course without spending time outside the classroom learning and embedding the knowledge from the days sessions try and get into the habbit of this early on and it will just be routine for the later weeks . Also if you can when you get there try and learn how to use the sim including the back desk as quickly as you can as really the sooner you can be comfortable practicing on that even when the trainer isn't around the better . And dont neglect sim time even later on when you have exams coming up , I know it will be tempting to do so .
Also even if you feel daft doing it , if the trainer is going over something and it really is not making sense (particularly early on) make sure you ask them to put it in a different way or spend extra time on it . There is quite a lot of material to get through so if the trainer thinks everyone gets something they will move on to the next thing . Likewise if you are having any issues with anything make sure you ask the trainer for extra help , theyll put as much effort in to helping you pass as you are prepared to put in from the other side .