I'd suggest hiring a tutor, either a former/current teacher or a past HSC student who excelled in english (advanced), extension 1 or extension 2. You can't go wrong with 1-on-1 coaching and help.
I came first in my school (49.5/50 overall) but it matters more the rank than the actual mark itself...also, internal is only 50% at the end of the day....I just hope externals went well...hmmm....