Best agency to join for acting?

Look into MEAA. Here is how to apply for an agent.

http://www.youtube.com/watch?v=0nUBPVIwJTE

All the best :)

http://www.theatre.asn.au/book_page/actors_and_act...

http://www.theatre.asn.au/book_page/agents_and_age...

http://www.alliance.org.au/

Your teacher is right about the agencies, but for the best info, the above links will help. You need to get your parents involved. Starnow and Starcast may be worthwhile signing to (personally I don't think much of them, but some actors recommend them), but won't actually do anything for you. That is, they're just sites where you can browse auditions that are posted openly on free sites (so why pay?); they can be full of scams or scary people; just because you have a profile there doesn't mean you'll get noticed.

Far better you get an actual agent.

I'll assume you're doing a short course and not a full-time uni degree, because if so NIDA should be providing info about agencies anyway. If it's the former: go read the three sites I posted.

I cannot find a web site for NIDA that would be what you are doing. Starnow and soon are rip offs doesn't your teacher know that? And agency fees for speaking roles are ten percent, have been for years and years. You need four things to submit for representation by an agent (you don't just go pick one and join--they select you, not you select them). 1. a resume of all the plays you have been in, the professional classes you have taken and skills you have that would be useful in acting. 2. a head shot 3. a cover letter 4 your parents who have to write the cover letter and sign for you until you are 18. Sometimes it takes years to get an agent.

SAG website.

henderson's book

callsheets.