Well, a good way to start would be reading past essays to get an idea for the structure/language being used. Also try to increase your vocab - look up words in the dictionary and try to find more interesting synonyms.
For each specific area in english:
Language Analysis:
- write heaps of practice essays
- go over persuasive techniques
- use the DEER method to begin with if you're unsure - Device, Example, Explanation, Reader Response
- get your teacher to look over your essays; do this a couple of times before a sac
Text Response:
- again, heaps of practice essays, and get your teacher to look over them
- a good way of studying for english is topic tracking - work out the important themes of the text, find where they are reflected, and analyse those sections. You can find a lot of great quotes/structural elements to use in your essays that way. Start by working out the important themes of the text, and then look carefully for moments that really encapsulate these notions. Take note of these sections and analyse them; highlight good quotes, pick out structural components that you can use to talk about the author's writing technique; by the end of year 12 I had a set of examples I knew really well and could use in basically every essay I wrote.
- make sure you have at least 3 quotes in each paragraph, and try to incorporate a structural component in each paragraph
Context:
If you're doing expository (which is all I can really help with), then...
- again - PRACTICE ESSAYS!

and annoy the hell out of your teacher by showing up to his/her office multiple times before your sac to have your essays read over
- pick out a few examples from the text that reflect a wide range of prompts
- do research to find events/literature/films,ect. that reflect your topic (encountering conflict, imaginary landscapes, ect.)
- and now the most important - write one really great piece that you're happy with, and try to re-write the same piece for a different prompt - make changes where you can so that it fits with that prompt, but try use the same examples. By doing this, you'll easily be able to respond to a number of prompts, and it'll save you a lot of stress during the exam

It's also a good idea to have this looked over by a teacher - if they are happy with the ideas/examples you've used, then you know you're in a good place for the sac/exam.