This is the worst study advice ever.. but honestly, if you dont plan on going to uni, but tafe, DONT get a UAI.. do what you need to do to get your HSC (Requirements), and you will get into any course.. just answer all of your questions in the exams, Make sure all required assesments are at least completed, and you will be fine.
Remember, youre only young, you dont need to jump into UNI right after school.. you deserve a break after 13 years.. id advise getting a part time job and/or do a TAFE course of general interest/in something you want to do or are interested in.
I just did a Radio Broadcasting certificate at TAFE after being slack at my HSC.. they wanted a HSC.. well i had one. Im applying for AFTRS for 2010. Remember;
ANY HSC IS BETTER THAN NO HSC.
Also. if you dont go for a UAI or dont get the number you were aiming for, not all hope is lost.. you can do a course at UNI for a year that will get you into pretty much anything you want.. what you got in your HSC doesnt matter.. imo its better than just jumping straight into full time study without any kind of 'break'.
I know all of what im saying 'isnt the right thing to do' but i just feel for people that are just there because they dont know what they want to do, but know they wont be doing uni in a hurry.. Well it worked for me. I didnt study at all for my SC or HSC, and i got both easily. i just turned up to class almost every day, was polite to the teachers, did everything that was required of me, and most importantly, I BAILED on my UAI (trust me you'll want to do this if you dont want to go to uni and wanna slack off, its unfair for your peers)
I'll tell you what my principal said to me when she had a chat mid year 12 last year..
(Paraphrased) "What do you want to do next year.. TAFE? cool, well you could do better and should, BUT what youre doing now will get you into what you want to do at TAFE."
Just dont stress it, be chillax, and you should be fine!