While standard English is spoken in most parts of the city centres, as soon as you venture a few kilometres from the city, your understanding of the spoken language around you will drop, unless you're familiar with Australian slang. The further out you go from the city, the more slang people use. Take a Captain Cook at these links to find out more.
Sydney talkback station - listen live
2GB Sydney talkback station - listen live
Want to get an idea what the local lingo sounds like before you visit Australia? Listen to the major Sydney talkback radio stations online before you go. (Try and understand Australian accents before you get to Sydney!)
Lot of information about Australia slang and guides on how to communicate with Australians.
Planet Guide to Australia
Plan on backpacking around Australia? Want to experience the local culture? Then Lonely Planet Australia is the book for you. Covering the basics of almost everything in over 1000 pages, Lonely Planet Australia will help you save money, time, and stress. If you're looking to have an expensive holiday then you won't need this book as it focuses on the things you can do in the back streets, hostels, pubs and other exciting and dangerous places in this English speaking country. For the younger traveller who wants to have fun. Note: to fit all the information in the print is quite small and the maps are fairly basic.
Lonely Planet Guide to Ireland
Visiting Ireland? Hope to be able to have a Guinness in the pub with the locals? You'll have to understand the local culture first. This is the book to help you.
Other English speaking countries guidebooks:
Lonely Planet Britain - Lonely Planet New Zealand