Heya - I started by going to Actors Management in Perth. This is an agency which also hold classes for kids to adults on acting for the camera. They were very benificial...up to a point when i left and took on the theatre. Like the person before me said, if you don't live in Perth, i can't really help you out with places, but if you do, you can also check out the WA Youth Theatre Company. I'm a member and have done quite a few shows and classes/workshops with them all around perth.
The best way to get started is to get experience. So once you join classes and/or companies, do as much as u can. it really pays off......hardly ever financially, but on all other terms it does.Good luck.
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