What structure should I use for A-level English essays?

So, very similar to GCSE, the essay should be split into three main sections: introduction, body and conclusion. When answering the question, the number one key is to engage with, and analyse the question. This goes for all subjects, but specifically English where essay questions often ask you to address an entire genre in your answer. Analyse means "to break down", and that's what is essential to start your answer. This is where you can start to write your introduction. Your introduction should include your breakdown and answer to the question. If the question is "To what extent does Othello take on the role of a tragic hero?", your introduction should set out the criteria for a tragic hero, which makes it very easy for the body of your essay to go through these one by one and argue for and against. It is also essential that you answer the question in your introduction. As my English teacher used to say, "essays aren't crime novels". What he meant by this is that examiners do not want to wait until your conclusion to find out "whodunnit". Instead, you will earn far more marks by setting out your answer in the introduction, and then constantly backing up and making your case stronger and stronger throughout the body of the essay. A nice way to wrap up your introduction is to signpost what your essay will cover. Very briefly outline your main points and then it is much easier to refer to this for structure in the body of your essay. 

In terms of the body of the text, use this as an oppurtunity to show that your argument is completely infallible. It might be that your argument is that "no one knows", or "it is impossible to decide", but make sure you take the oppurtunity to show why that is the case. You're looking for approximately 3-5 strong reasons, each taking up a paragraph, and often it is a good idea to include counter arguments within those paragraphs. Use counterarguments to back up your argument. Instead of saying "some might argue....", say "some might argue...however." This way, you show the examiner you have an understanding of other perspectives, but your case is the strongest. Each paragraph should end with a reference back to the question, ideally you saying that this point shows your case is the best or strongest. Finally, a brief conclusion paragraph should simply some up the strongest elements of your argument and wrap up the question - "because of A and B, the answer is clearly C". Do not include new material in your conclusion, just a very brief summary to completely confirm your case.