Learn the local language
Australians speak English, but they have their own slang vocabulary that dominates their conversational Australian English. You can find yourself in the unusual circumstance of speaking the language but not understanding what they've just said. So, to assist you, here are some key terms to remember: Togs/swimmers/bathers = bathing suit; tomato sauce = ketchup; chuck a U-ey = make a U-turn; "Would you want to join us for tea?" = "Would you like to join us for dinner?" Remember those and you'll be OK, but don't be afraid to ask questions; most Aussies will gladly interpret — you'll be fluent in no time.
It appears that having various spellings throughout countries wasn't enough for some folks; they went the additional mile and altered certain terms totally. You may be familiar with some of the more well-known ones, such as "fries" in America vs "chips" in Australia, but there are many more. However, there are several that you may not be aware of. If you ask for "gas," you could get a raised eyebrow because the Aussies call it "petrol." If you ask for a "trashcan," you can be jokingly referred to as a "rubbish bin." Are you looking for "candy"? Request "lollies."