first bit: I mean that although in-depth understanding of the text is crucially important to doing well in english, there are also other aspects which you can only really get from innate ability or extra exam practice. You need to be able to come up with a thesis (hopefully you've already got opinions on it) which is appropriate to the question, pick out the relevant bits of information to base your introduction on, write quickly and coherently, and formulate an argument logically using appropriate language.
They are allowed to ask you any for any specific text form on the day (even though it's usually pretty generic because it's the same exam for the standard students), to write about any particular character or scene, to argue a particular side of the case. It's not as easy as you'd think to come up with ideas for a feature article or a speech in 5 minutes. It helps to have practised a wide range of questions and text-types, to have written an essay from the opposite perspective, etc. This way you know that you've got all your ideas in order and won't falter on the day even if the question throws you a little.
You also need to have a good understanding of the unit of study and what's in the rubric for assessment (can lose you a LOT of marks eg. decent essay gets you 5/20). You need the understanding of the text to do this, yes, but you also need to be able to juggle your exam technique quickly and effectively, and the best way to learn this is to practise. The people who did best in english were always the ones who had practised heaps of past papers, gotten feedback from the teacher, rewritten until they got 19 or 20/20 for them, and learned that way.
second bit: I know some people have done quite well pre-preparing essays and modifying them to suit the question. I don't agree with using this method so much, especially with people memorising generic essays almost word-for-word. I think the best responses are always going to come from good understanding of the text and how to apply it to the question. I don't think doing a lot of past papers is necessarily pre-preparing essays, but it helps during an exam when you get a question that you've done something similar to before, and you can think back to the feedback you got and not make the same mistakes again, not try to use arguments that you later realise you can't support, etc. And as I said before with the text types, if they ask you for a speech or a feature article or an interview or something, and you've never tried to write one before, you might be in for a rough time no matter how well you know the text.
So there's my answer. Sorry it's a bit long... x_x
and my exam tip for today: the introduction is worth a lot. A bad introduction will give the marker a bad first impression, and they're only spending like, 10 minutes reading your paper, so that's not good. Do it well.
