Hey bro,
It is very good Idea to study two subjects a day, so that you can study the sciences in one day and Maths in the other day, in terms of practicing alot of questions and writing good notes for the sciences. You could then study the English in the third day, by organised your essays and practice HSC style essay questions to mould you essays to them.
Some of my friends who are now doing medicine and law course have done, this and they said it allows to concentrate on each subject a day, which really helps you to stay organised throughout the year.
Personally, I study two subjects a day. For your sciences, it is a very effective and efficient to get a separate book and download the syllabus for each chem and physics and stick the doptpoiunt at the top and write all your notes, epquations/graphs below it. This way your making notes that are very effective for memory retention and well organised by the time you head the trials. Constantly review these notes and do practice questions as soon as possible.
For maths ext 1/2, learn the concepts properly and again try to get a different book and write all the formula's you need for each topic and find some hard examples for each topic from different textbooks. As this allows you to look for repeating in HSC style questions and also helps you to understand what questions they might throw at you in the HSC.
English Standard doesn't scale that well, but if you do well, it will scale well ( I mean try to be in the top 3 and ace the HSC exam- bam 90+ HSC) Write practice essays each day and look for feedback till you teacher says, its good for full mark, never try to memorize anything, you can adopt your essay to any questions, if you have written a good essay.
You could get 98+ Atar, if you do extremely well in each of your subjects.
Good luck, lol