A 91 ATAR is definitely achievable with your current subject selection. In order to ensure that your performance across your subjects is consistent with your ATAR goal, you must ensure that you are committed to each of your subjects, which involves developing a study plan that will effectively meet your needs in terms of each subject.
Favourable performance in maths requires that you have a good understanding of the concepts and ensure that you can apply your knowledge to different types of questions. This is why it is essential that you complete a range of practice questions that can be found within past exam papers from different schools. Doing so will enable you to identify areas of weakness and will subsequently give you the opportunity to rectify them (if applicable). Completing numerous questions from different past exam papers will also maximise your exposure to different types of questions, consequently improving your ability to effectively manipulate those concepts and hopefully leading to superior performance. It is important that you seek assistance with any concept(s) that you feel you are not sufficiently familiar with or do not fully understand.
In order to maximise your performance in English Standard, it would be a good idea to ensure that you are familiar with your prescribed texts, including themes/ideas/issues raised in each and their relevance to their respective module. Additionally, it is also important to be familiar with a range of literary and visual techniques, including what they are and the effect that they generally present when included in a quote/text. This will enable you to enhance your analytical skills, which can also be supported by completing a range of short answer questions in response to unseen texts. To improve your writing (in terms of your essays for instance), you should regularly seek feedback from your teacher and implement any suggestions that they offer.
Performing well in Business Studies requires that you are familiar with the concepts/topics and can apply your knowledge of the content to the different types of questions that can appear in a Business Studies exam/assignment, such as multiple-choice, short answer and/or report/essay questions. To do this, you may wish to regularly revisit content that you have covered to ensure you maintain a good understanding of particular concepts and, if needed, seek assistance with any concept(s) that you feel you are not sufficiently familiar with or do not fully understand. Completing past exam papers is also beneficial in terms of ensuring that you can effectively apply your knowledge of Business Studies content to different types of questions, such as assessing your knowledge of financial ratios.
Of course, laziness and poor time management cannot be immediately eradicated. Instead, gradually adopting good study habits will ultimately allow you to become a more committed student who can manage his studies well. You may wish to start by covering a bit of each subject every day. If at some point you feel that you can handle additional workload, then this is likely a positive indicator. Lastly, BoS is a good place to seek assistance, especially with subject-specific concerns.
I hope this helps!