There's no set formula to follow when writing a great essay. I never really mastered the art of analytical compositions in English (hence I got a mid-range band 5 for Advanced English). Here's what I tried to practice when writing Senior English essays:
You have to work to your strengths. If you have a good vocabulary then use it! If you are good at constructing sentences then experiment with your sentence structure/increase complexity.
Before you start writing your essay, know exactly what you want to say. Don't improvise as you go. This is where essay plans become essential. You should be able to summarise the crux of your essay in one simple sentence (this becomes your thesis statement).
Be original with your use of ideas and your writing style. You don't need to be crazily post-modern or overly sophisticated (which is actually worse then being overly simplistic). Do something a little out of the ordinary to stand out. Perhaps you could start/finish your essay with a powerful quote from the text or a famous quote/philosophy which relates to your thesis/essay question. You could write out your thesis 5 times using different words/phrases so you when you repeat your thesis at the beginning/end of each paragraph it is slightly different (but be careful, sometimes changing the words in your thesis changes the meaning too much that you start arguing a different thesis).
You need to address the concepts in the course outline/rubric/syllabus. The easiest way to do this is to make a glossary of key words/phrases and use them in your essay. E.g. for belonging, words like acceptance, identity, alienation etc are all specified in the rubric so you should discuss them!
Make every word count. If you are writing words simply to fill up lines then the words are not worth having in your essay. You are better off going back to your plan/thesis and seeing what you need to do to get back on track. In other words, don't waffle, it is one of HSC English's cardinal sin. Other cardinal sins include over-prescribing (rote-learning essays and replicating them in the exam regardless of the question/textual form) and not including techniques. If you do not analyse techniques, you will not get higher than a C grade.
Small, logical paragraphs are better than long, complex ones. One key idea per paragraph. Once you have your main thesis statement you can create further sub-thesis statements (closely related to the main thesis statement) which become the opening/closing sentences of your body paragraphs. This will help you to have one key concept per paragraph.
Don't be afraid to argue a point which is obscure or out of left-field. If you it off you'll stand out from the pack. Think about it, what makes a more interesting essay: Belonging is about the celebration of cultural identity OR Belonging is societal contruct, meticulously woven into mainstream culture?
To close, you need to do a lot of practice to bring yourself up to a band 6 level (if you're not already there). Essay writing is a skill, an art-form. Practice perfect makes perfect. Write an essay, get your teacher to mark it, edit the essay based on the teachers comments, get another teacher to mark it, do further editing etc (if you get the pattern). Keep doing this until a teacher tells you its at an A grade level. This could be a very long and tedious process but your effort will pay off. Generally speaking, those who achieve the top bands in English are persistent and determined, they are active in their learning and they keep striving to improve. Even if they are already a brilliant writer, they still wish to iron out any small weaknesses and turn them into strengths.