From looking at section 1 of HSC & trial papers for the Area of Study, examiners are most interested in the following ideas about discovery and as such, they will choose texts which explore these ideas:
1. Self-discovery by way of an encounter which compels the individual to confront a repressed aspect of self - either a cultural identity, or certain wishes and needs that do not conform to society's norms and ideals.
2. Seeing other cultures from a perspective that goes beyond mere stereotyping or preconceptions informed by experiences with one or two individuals who represent that culture.
3. Reflecting on long-held convictions about an issue (revenge for instance, as we see in
The Tempest), another individual, or a group, and having to revise that conviction after a spontaneous experience which challenges it.
The best way to prepare for the unseen texts section in my opinion is to think about those ideas and really figure out what they mean by looking at how they are exemplified in your prescribed/related texts. Then compile a list of visual, poetic, and narrative techniques and practice identifying them in the unseen texts of past papers (all available on the BOS website).
Go into the exam with 1. a set of ideas of discovery which cover a wide range of discoveries (such as those mentioned above), and 2. a set of visual, poetic, and narrative techniques.
Before the exam you should do at least two practice papers and apply those techniques and ideas to the unseen texts in those papers. If time permits (and it should! don't leave this to the last minute), check your answers with a teacher or tutor. If you head into the exam with a good arsenal of ideas, techniques, and have practiced applying them to different visual, poetic and fictional pieces under time constraints, you should do well.
If you haven't seen this already, I have some examples on how to apply ideas and techniques to unseen texts
here. And some tips on poetry analysis
here.
I'll PM you a couple of guides on analysing poems & narratives from the first section of a past HSC paper when I'm done editing them.
Hope that helps.