For Bio and Ancient, I found studying my notes really helped.
Once I was fairly confident I knew my stuff, I managed to get a hold of as many past papers and practice questions in the HSC style and worked through them all. (But never do them all at once. Start with older papers and work your way through to the most recent. Don't rush through them in one day, spread it over 4-5 weeks prior to the HSC. If you can, work through each paper as though your in the exam, so 3 hours at a time.)
Where I made mistakes I would go an review more, and where I had consistently done well, I wouldn't focus on as much. Then as I did more papers, I became more confident in my writing and knowledge of my topics.
Knowing your content is extremely important, but can only get you so far. With Ancient in particular, to get a higher mark you need to be able to construct your written answers well. So being familiar with the style of questions and what is expected of your answers can also help you.
Personally, I found a combination of both revising my notes and doing past papers was essential to achieving the marks I got in both Bio and Ancient.
Hope that helps