Awww...Jack sounds like me 20+ years ago.
Best advice is to get experience dealing with people...both customers and colleages. Be comfortable/confident with strangers and be able to feel at ease/conversing/interacting almost immediately. If you can't get a travel related job, retail is a fab start.
Start keeping a log of "situations", such as when you've dealt with a difficult customer, when you've had to provide excellent service (and what made it excellent), when you've had to work as a team member (and what your contribution was to the team), a situation where you've had to give feedback (and feedback to someone who was your supervisor), when have you had to deal with conflict (and how did you deal with it), when have you had to deal with someone from another culture/background. These are questions that many cabin crew selection days incorporate. Once you've got the job, try and keep a log of "situations" as they will come in handy when you go for promotion.
I starting flying 18 1/2 years ago, when I was 20 and It has been the most brilliant lifestyle and career choice. I've travelled the globe, meet the most interesting people, and along the way learned what's really important to me as a person.
I wish you all the best in getting into Qantas, but don't dismiss other airlines out there. Glad to see the enthusiasm for the job still exists.