theres a HUGE young aussie community in london. HUGE. something around half a million estimated. Live in a hostel for the first few weeks, get a flat with some people you were there with (happens over and over, and seems to be the best way I think).
Also, you want to peruse TNT magazine, its free and comes out every monday, has pretty much everything you need in it. Its an ozzie/kiwi/saffa mag for people doing what you're doing, although I admit I used to read it avidly. Oh tnt how I miss you. Its got news from home, and travel deals, and job listings, and club happenings, and desparately seeking. Everything.
Also, thegumtree.com is a treasure for finding jobs. Seriously its amazing and you might have thousands of job postings in a day. They post jobs for out in the country in the UK, and honestly as much of an awesome time as I had in london I wish I'd've gotten a pub or farm job for a bit just to experience it. London isnt really britain. But its really easy to travel to all of europe and beyond from there. And you cant beat the vibe. Try to put your name in a few recruitment agencies, too. I also have a number for a most excellent woman who does nothing other than give young fun ex pats job hookups. I'll pm you with it when I find it in my shit.
Have your CV already made up before you leave, one page deal is fine and send it as an attachment to yourself by email so you dont have to cart it around. I can send you mine if you want a template. When you go to interviews, even for bar work etc dress very smartly. And try not to live where you work. It seems like a great deal at first, but eventually you come to the realisation that your boss somehow knows every single thing you do, when you come home late, when you're drunk, if you pull, and its sort of creepy and bizarre. Really creepy and bizarre.
Thats all I can think of at the moment, really if you want to save money I say live outside of london because it is an extravagantly expensive city and its like your money evaporates into thin air. Look into working for a YHA hostel, they can place you all over the UK and working in a hostel is well if nothing else very interesting and gives you no end of good stories to tell. Im an american, so I guess my experience was different, but I'll try to answer any questions you have.
The most important thing is to have a good time and make friends.