Yes, it is definitely possible.
The keys to English:
Step 1 (preparation) - people prepare in different ways but the most common form of preparation is a 'generic essay' so to speak.
Others prepare by just preparing textual evidence or paragraphs of analysis as opposed to an entire essay.
If you're the type of person to prepare generic essays, you should aim to refine it over time (have a look at exemplar band 6 level essays and see what they did well - however, don't plagiarise - and gather and incorporate feedback from your teacher or tutor if you have one). It's obviously better to go into an exam with better prepared material than worse prepared material.
If you have a good level of preparation, half of the battle has been fought. High quality preparation is essential in any subject, same goes for English.
Step 2 (practice) - students who dump their generic essays onto the paper are usually limited to a band 3/band 4 (depending on the quality of their prepared material). Band 5 is somewhat possible (especially for 'generic' essay questions) but if you want a high band 5 or a band 6, the key is how well you answer the question.
Practise your ability to mould or adapt your essay to answer the given question if you're the type of student who prepares generic essays.
Pick a few past HSC/trial questions and try to answer them (either mentally or you can actually write full essays if you have the time). This will enhance your ability to answer the given question (with your prepared material) on the day of the exam.
One of my friends went from getting Ds in Year 11 English to becoming a band 6 English student in Year 12.
The reason for his transformation? He just improved his preparation (from winging essays in Year 11 to having high quality prepared essays in Year 12).
Preparation and practice.
Studying for English isn't as complicated as some students make it out to be.