You should probably go in with a prepared essay but you should leave some word space maybe like 100-200 that on the day you can use to analyse whatever part of the text you will be listening to, because it's important that you incorporate the extract they give you in the exam as a core part of your essay like mentioning it at least 1 or 2 times a paragraph or writing an individual paragraph on it that links to your prepared essay. If it's a film maybe try to just write down some extra techniques and analysis from scenes you think are key to the story because they will probably choose one of those