By now you should have already started some past papers whether it be trial or HSC, although I didn't do this, you should do other schools past trial papers first then drawing near to the HSC exam to the past HSC papers so you can get a feel of the actual HSC papers, but I did it the other way around, which didn't matter in the end if you can recognise the structure of the HSC papers and types of questions they may throw at you.