As in previous editions, Cyclecraft provides very useful advice on road-sharing in general, and detailed advice on how to recognise and negotiate hazardous situations, cyclist-hostile road designs and pretty much all pitfalls and obstacles. Its scope is comprehensive and its style is admirably clear.
The advice to keep your bicycle well maintained is spot on, though you'll need a different book if you want to do such maintenance yourself; this book focuses almost exclusively on how to travel safely and enjoyably.
Since it's published in the UK, the text assumes you will be travelling on the left side of the road. The text is certainly broadly applicable to the Republic of Ireland as well, though, as another reviewer says, the law in the Republic of Ireland currently compels cyclists to use cycle tracks. Given that, the advice in this book on how to negotiate the poorer designs might actually be even more useful there.