How do I structure an A-level English essay?

A method that works for me is highlighting the key terms in the question and then approaching it thematically from there. Let's take the question 'Compare and contrast the presentation of marriage in A Doll’s House and The Merchant’s Tale' as an example. Here, the key terms to highlight would be 'compare', 'contrast' and 'marriage'. The focus of this question is 'marriage', so you would start thinking about different themes that relate to marriage in both texts, as you will need to 'compare' and 'contrast' them. For this question, I would focus on 'controlling husbands', 'deceptive wives' and 'the idea of marriage as a performance', as these themes appear as important components of both texts. I would then find supporting evidence from the texts for each theme to create a strong argument and comparisons, as well as relevant critical material and contextual points. It is important to begin each paragraph by clearly stating the point of the argument that will be discussed, and conclude each by with a sentence tying the main points back to your argument to ensure your essay remains focused on the rubrics of the question.