Believe it or not, this point is not for non-English speakers. I've found English fluency will not help you much here because there's Aussie slang or abbreviation for just about every word in the English dictionary.
The slang often follows two principles: Shorten the word and make it much more fun to say.
Tons of Australian slang involve shortening a word to its root and ending an -o suffix, like servo, arvo, avo, smoko, and bottle-o. Those were: service station, afternoon, avocado, smoke session, and bottle shop (liquor store).
However, memorizing those principles alone won't be enough to get by. Aussies change McDonald's to Macca's, mosquito to mozzie, breakfast to brekky, cooler to esky, and so on.
I recommend looking up a list of Australian slang words and memorizing the most common ones before you visit. Over time, you'll hopefully get the hang of it.