Drinking in Australia is incredibly easy. There are more pubs and bars than there are places to eat, which demonstrates how Australians prioritise their nourishment. If, however, you have any trouble finding a pub, knock on the door of any building and the occupant will not only tell you where the closest pub is, but most likely offer you a traveller - a beer to be drunk on the way there.
Ordering a drink
Beer - There is a vast array of different glassware from which beer can be consumed, ranging from the mouthful-sized pony, to the ludicrously enormous birthday pot. Choosing a size is not easy, as the same size will have different names from state to state, and the same name can be applied to different sizes of vessel in different states. Just ask for a middie (285ml, or about half a pint) until you have a confident grasp of the local terminology. For example, in Victoria, a middie is called a pot and in South Australia it's a schooner. In New South Wales, a schooner is 425ml, and a pot is something you put plants in. There's no need to specify any particular variety of beer, as you will automatically be given the most popular and affordable brew.
Spirits - Order the spirit first, then the mixer. This rule is not absolute, but anyone that asks for soda and whiskey or soda, lime and vodka will be thought of as Norwegian and/or a moron.
Wine - Most of the major city drinking establishments will have absolutely no problem serving you wine - indeed, most will have impressive wine lists. Country pubs will have white and sometimes red, both from a box.
Soft drinks - An order of a non-alcoholic beverage must always be followed by an apologetic, "I'm driving".
Paying for your drink
Cash is always a good starter. Australian currency is a must, unless you wish to have large denomination US dollar bills exchanged at horrifying rates. (Any bar tender in Australia will happily exchange 100 pounds or US dollars for 100 Australian, which are the only two denominations they know they can double their money on.) Always have your money ready.
Visa or Mastercard are usually accepted when running up a tab at the bar, but not for one purchase at a time.
Tipping is not compulsory in Australia, and is usually received in the same way that one would receive charity, i.e. badly and with forced gratitude.
Returning your glass
This, also, is not compulsory, but is received better than a tip. There are four ways to place the glass on the bar top:
Empty, upright, money alongside - This signifies that you would like the same again please. Feel free to turn your back, talk to your friends, whatever. Nobody will steal your money. Anyone that does will, if caught, undergo extensive facial re-arrangement, which is why nobody does it. The next time you turn around, you will see your drink, and the correct change.
Empty, upright, no money - This signifies that you desire interaction with the bartender. This may be for a query, a different drink to the last one, or a cricket score.
Empty, glass laying on its side - I'm off now, no more drinks, pay no more attention to me. (This simple gesture is also generally received better than a tip.)
Emptyish, upside down - Traditionally, this indicates that you would very much like to fight everyone in the establishment, and that you think you could win easily. Never, ever do this, even jokingly. Australians do not find it funny at all. Most of the time you will not get into a fight, unless you fail to notice the seething hatred and utter contempt emanating from every individual in the vicinity, and do not leave immediately. If a fight does start, you will have to fight everyone in the pub, until you are deemed to have taken sufficient punishment.