Read notes/textbook and examine the syllabus. Make sure you can answer every dot point on the syllabus and actually understand it too and to make sure you understand something, make sure you can explain whatever it is to someone clearly and LOGICALLY. E.g., your friend asks to you why a catalyst is used in reactions. If your answer is just to speed up the reaction, then you haven't understood this concept. Need the reason why it speeds up the reaction.
Most of chem is lots of memorisation of facts about chemistry, which tend to get boring...
Once you get the content down, you MUST APPLY it (which is the hard part in my opinion) by doing practice questions/HSC QUESTIONS
TIP 1: constantly test yourself to see if you understand/remembered the content - good way to learn
TIP 2: if you have the motivation and energy, then try this routine out: after everyday you learn chem, get a blank sheet of paper and without the aid of notes, write down everything you learnt that day - I did this for 2 days and it was EXTREMELY helpful but I couldn't do it anymore because it took out most of my energy. You can do this routine monthly instead of daily, up to you to decide
TIP 3: when marking your own completed past papers, mark as harsh as you can so you can identify your mistakes and fix them
GL!