Being from Australia i sat the high school certificate, also known as the HSC and went through many exams of all subjects including modern history, ancient history, english advanced, mathematics advanced, economics and business studies. The HSC itself is an accurate grading system, presuming class grading is consistent with exam marks. I have some short advice when completing HSC subjects to maximise exam and assignment marks.

English Advanced. Make sure you maintain good structure throughout all your answers. Start with the introduction, bring in both sides of the argument, use quotes and have a strong conclusion. Staying to this structure will ensure good results.

Mathematics, advice for both general and advanced. A lot of study is needed before exams for this. Doing past exams also helps a lot with mathematics.

Modern History. Learn a lot of facts. Structure is good to have. With a lot of facts your essays and assignments go to the next level, which is good.

Economics. A lot of pre exam study works well. Also swap notes with classmates and refer everything to real world examples.

Business Studies. Do a bit of fact study. But also spend a lot of time going over past exams and case studies. Being able to relate it to real world business examples is really important.

The best thing to do with the HSC is to choose high scaling subjects and work hard to get good class ranks. Then some solid exam marks should put you in a good position.