Over the last few years I have travelled quite a bit in Italy, mostly by train. Despite what everyone says I think it is a really good service and very economical. It can however be a nightmare to work out how to actually get to where you want to go (especially if you don’t speak Italian!) and to work out the fine print of prices, regulations and all other crazy stuff you only find in Italy.
I have found that the timetable you can buy at most newsstands is very helpful and, to my knowledge, almost always correct. It only costs about 8,500-12,000 lire and comes out twice a year (winter and summer). At first it may seem hard to follow but it is invaluable because it saves the agro of asking sometimes irritated FS officials for information or missing connections etc. It just makes the whole system manageable! I suppose it’s not that useful for people in Italy only for a short time but for anything more than 3 weeks I would recommend it. It is usually called something like “Pozzorario delle Ferrovie Italiane” or something similar.