1. Writing a very good paper on the day is seriously the key to getting a 50.
I was not ranked no.1 for sacs - yet got 50 - in fact I'd say I was probably ranked somewhere in the top 10, certainly not the top few. But as my English teacher said - my SAC marks were solid - so A+s of various levels.
2. Absolutely know your texts intricately - forget the bull that you don't need to study for english. I'd seriously recommend reading them 5-10 times. The first read for 'pleasure'. The next few to kind of get your baring in the book - start thinking about what's important, main issues/character development. I would also then sit over about a week reading it with a computer and noting anything - quotes/phrases etc that I thought might be useful such as 'everything turned into mist' or something from 1984 that I remember still now. This approach means you don't actually have to memorise quotes, as they will literally just come to you.
3. Work on basic essay things - know how a good lang analysis works for you; a good context piece and a good text response. My lang analysis tasks contained lot's of sentences/corresponding sentences that consider what the author does "by doing x', the effect of that and then how it would impact the reader.. (yeah hard to elucidate in the abstract).There was a really useful document on here written by someone who had put a page of words useful in certain circumstances - for example connoting/elucidating/evokes/ by juxtaposing etc - that I found useful as a guide when writing to think of how to attack an piece. There were words on it that I would never use in my own writing, hence wished not to use willy-nilly in my pieces, but I am a firm believer that lang analysis is a test of both your ability to analysis the text and use language fluently and effectively yourself to describe something somewhat mundane usually. My context pieces I only nailed an approach literally a week before the exam - it had been absolutely irritating me prior to that point -was so unsure (plus I did it in the first year of the study design) - generally I would have Bruce Dawe/old man essentially reflecting on his life as an old man which meant that you could throw in lot's of things about I&B and overtly be referring to the poems without making it too text-reponse like. As for text responses - need to know how you conclude/introduce your essay (obvious I know) - but I emphasis you need a model that works for you and makes your entire essay persuasive.
4. Don't become stale by doing too many practices. Yes - I am advocating not writing 30 essays prior to your english exam. I am advocating at most 3-4 from the term 3 holidays for each area. This will probably be a contentious issue but what I found infinitely more beneficial was actually doing plans. I did around 30 detailed text response plans on a wide range of essay topics - I found this really useful as it would mean that an area you hadn't considered would be explored - most of these plans were about a page in word. It was good because you could literally work out the subtle differences between arguably identical topics. I did this also with prompts for context - trying to work out what you vaguely would discuss and found about 5-6 general areas that were recurrent and knew what sort of approach and which poems would be useful in such an essay. As for language - I literally would get a sentence from something and analysis it to the extreme by considering all the words.
Hopefully there is something useful in there - but do work consistently. Read well, read widely and build an interpretation of the text for text response.