As others have said, circle geometry is often asked under harder 3 unit. They can be tough, so here are a few pointers:
-Know all theorems well, and do lots of practice.
-If stuck, leave it and come back at the end.
-Draw a really neat diagram, and preferably don't scribble over the exam paper one, because it can become obscured, and you wont be able to draw a new one accurately if you need to.
-Use all the information: they wont put in anything you wont use, therefore you can sometimes use information given as starting points, although they seem to be unrelated to the question.
-You can work backwords from given info, just like in inequalities. Eg if these angles are equal, then the arcs on which they stand must be equal, and so on.
-Look through the proof of some common results, eg incentre, circumcentre, and so on. Although they wont be asked in hsc, in trial papers they are. The example dreamerish gave is a common sort of question.