For those who aren't naturally talented, it's perfectly viable to memorise essays and change perhaps the first and last sentence of each paragraph, and slightly alter the introduction and conclusion to fit the topic/prompt. I pretty much did this and it served me well. But note that when I say memorise, you don't necessarily sit down and rote learn entire essays. After having written a lot of essays, you will be able to recall your points and phrasing for just about any idea that you want to write about. The thing with writing a 'memorised' essay is that it still has to be relevant to the topic, so you basically just copy and paste a few paragraphs that you've done before which are relevant to the topic. Under no circumstances should you ever go off topic though because your marks will just plummet once the examiner knows you're writing a memorised essay.