Nothing wrong with reading the rule book ahead of your training, you'll have to read it at some point. Just be aware that most of what you'll need to be doing on a day to day basis actually *isn't* in the rule book - in itself it has a fair few grey areas and a lot has now come out and is down to each individual train operator to set their own rules and standards. The rule book also contains a lot of "official" terminology, whereas the operating railway uses a lot of slang. There can be many slang terms for the same "official term"; it's a bit like someone from a foreign country learning Queen's English and then having their first holiday in Glasgow. It's also not necessarily easy to understand for someone not from a railway background - you have to almost have seen it to understand it properly.
Some folk do say don't read the rule book ahead of your training and just rely on your course; being walked through it in a classroom setting worked for them and that's fine. But different people learn in different ways and if you learn better by reading up and learning hard facts then there's nothing wrong with that either. The training course will then teach you how to apply those hard facts in real life. Don't waste your time going through the rule book, not understanding it and still trying and failing to commit it to memory though, you won't learn anything like that. To properly understand and apply the rule book you have to understand the 'whys' behind it.
