At the start of year 12 I was getting 37% in maths!!!!! oh god the embarrassment...and then in the HSC I got 82...and the solution was...I got a tutor lol
But if you don't want to do that...then like everyone else is saying just keep doing questions. Excel is good, but it does get boring after a while. The examples are good so use them. Also, your teachers are one of the best resources (unless you have a crap teacher) so always ask them to help.
Use different colours when doing notes, it helps stimulate the mind. One thing I think is good, you may not agree, is to do past HSC papers at the start of term 2, then mark them, then do them again before the HSC and you will see an improvement hopefully. Do the multiple choice on the Board of Studies
http://www4.boardofstudies.nsw.edu.au/, it's more interesting than plain paper. And one thing to keep in mind is, 'the brain can only really concentrate on something for up to 40 mins' (quote my year 12 science teacher), so take a 5-10 minute break every 40-60 minutes, it's good for you and you will feel much better.
GOOD LUCK and remember don't stress, breath and relax!! The HSC is just an exam...not the end of the world.