I've recently seen an exam paper being shared on social media on which, after the usual questions, a page is provided for students to write down everything they know about the subject but haven't been asked about. I love this - I know how frustrated students can feel when they've worked so hard to know everything and end up only using a tenth of their knowledge, so it's great that they are being given the chance to show off. But it also speaks of a fundamental misapprehension about what exams are actually trying to do. Especially in the current circumstances, where most schools are telling students exactly what the focus of their questions will be, the process is not about testing knowledge: it is about testing the APPLICATION, ANALYSIS and EVALUATION of that knowledge.
The biggest problems identified by examiners and teachers is that students are liable to make lots of points, cram in a million technical terms and quote half the book, but none of this is done with any depth or purpose. Essays begin to look more like a list of ideas than a coherent argument. And an argument is what we're after here: a clear narrative that takes us from the Big Picture themes of the book to the specific purpose of language choices and techniques. Thus you may have a million interesting facts about Keats' views on nature and his use of natural imagery but in a question focussed on death, you may have to cast them aside.
This takes some guts: you will suddenly find yourself with three or four points rather than fifteen and this can be unnerving. But remember: three well established, evidenced and analysed points are a million times more valuable than twenty points on a ticksheet.
When I'm planning essays with students (something we do A LOT), one of the first things we do is... and bear with me here because this is going to sound ridiculous ... answer the question. I mean, yes, obviously, the whole purpose of writing an essay is answering a question but we start with our Big Idea, or hypothesis. Let me give you an example: a student asked about how Golding presents the character of Jack in Lord of the Flies responded by saying that he was a catalyst, producing discord that led to a shift from civilisation to savagery. First of all: what a complete star that student is (I've quoted her words verbatim - she is a genius). Second of all though: write it down. Put it in big letters at the top of the page so that you can't ignore it. Only once you've done that can you start to think about planning but crucially you are now planning with purpose: you are looking for information that supports the hypothesis you have formed. Now my student knows that, while the notes she has about violence and the death of Piggy might be really interesting, they don't actually help support the specific idea she is trying to put across. She is no longer going to write an essay which is a long list of "things about Jack" but now is going to use a few crucial moments which she can dig deeply into and use to create an argument.
Having a Big Idea in both English and History means that your writing has a hook to hang itself on. It means that your writing is focused, coherent and original. It doesn't have to be controversial or unique, it simply needs to be a clear answer. It can be nuanced; it can challenge the premise of the question and redefine terms; you can do what you like so long as the argument that follows supports it with logic and evidence. In History students are often faced with a question that asks how "successful" a particular individual or movement was. Here, a good hypothesis will consider the definition of success: is it defined by the individual themselves? By their legacy? By the extent to which they achieved progress? Thus your Big Idea will not simply be "yes s/he was successful" but instead "in terms of achieving the goals that they set themselves they were/n't successful" or however you wish to define it. Again, this means that you may have to cast aside some information that doesn't help your argument but in timed conditions this is to be expected: you are being tested on your ability to discriminate as much as your knowledge.
So before you start planning any answer to a question, take a moment and write down your Big Idea first - everything else will flow from that.