A high ATAR can be achieved with any combination of subjects. Although subject selection should not prioritise scaling (but rather interest, enjoyment and performance potential in the subjects in question), taking good scaling subjects, such as, in your case, Mathematics Extension 1, Chemistry and Latin Continuers can assist you in achieving your ATAR goal.
Regarding Mathematics Advanced and Mathematics Extension 1, it would be a good idea to equip yourself with a good textbook, such as Cambridge in addition to several past exam papers, which can be from your school or from other schools. Practice is essential in maths as it will enable you to apply your knowledge to a wide range of questions, which will subsequently allow you to identify and rectify any potential areas of weakness. It is also important that you seek assistance, preferably from your teacher, if you feel that there is any particular concept that you don't fully understand as soon as possible. All of this applies to both year 11 and year 12.
In relation to English Advanced, while there are no prescribed texts set by NESA for year 11, it would be a good idea to access the English Advanced syllabus document and develop an idea regarding what each module entails, including themes and issues. Doing so will guide your analysis of the texts that you will study in year 11 more specifically, both of which will provide a foundation for your writing. As you approach year 12, it would also be a good idea to access the Engish Advanced syllabus document and gain an idea of your prescribed texts (if you know what they are by that time) and familiarise yourself with the modules, including themes/ideas/issues that they raise. This will further support your analytical capabilities and will enable you to enhance your writing abilities. The English Advanced syllabus can be accessed using the following link:
Additionally, regularly seeking feedback on your writing, whether from a teacher or tutor is important and doing so throughout both year 11 and year 12 will allow you to make sure that you optimise your writing and constitutes good preparation in year 11 and will lead to favourable performance in year 12, where all of your assessment tasks/exams will count towards your results and ATAR.
In terms of Latin Continuers, ensure that you acquaint yourself to a high extent with Latin vocabulary and practice using the dictionary. This provides the basis for developing the skills needed to study the prescribed texts in year 12 course and to translate unseen texts. Additionally, should you wish to take Latin Extension in year 12, the linguistic capabilities gained in Latin Continuers in year 11 in addition to those that you will gain in year 12 can assist you in the study of Latin Extension, especially considering that the vocabulary in the Continuers course will be treated as assumed knowledge, since the aim of Latin Extension is to build on the knowledge and skills acquired in Latin Continuers. For instance, prescribed texts in Latin Extension, prescribed texts are representative of a major genre of Latin literature not studied in Latin Continuers.
I hope this helps!