How should I structure a response to a Philosophy/Ethics essay question?

I would always use an example with questions like this -- take the ethics question, '"Utilitarianism is the best approach to environmental ethics". Discuss.' Your first paragraph should be your introduction. Here you introduce the topic, for example briefly elaborating on the different facets of environmental ethics, outlining what is meant by 'Utilitarianism' as an ethical approach, and perhaps identifying key thinkers (Bentham/Mill/Singer) and their respective principles. You could also mention other approaches which may be worth considering in the context of your answer. The introduction is also where you outline the argument your essay will be making -- make sure it is clear and consistent with the body of your essay. The next 3/4 paragraphs (depending on time) should be the bulk of your argument, in this example it's where you explain and evaluate different ethical approaches to the issue of the environment. Evaluating utilitarianism should be your main focus: make sure to explain each utilitarian approach's nuances (e.g. Mill's distinction between high and low pleasures), how this relates to environmental ethics and an evaluation of its effectiveness for this issue. You should also include at least one alternative approach that is not mentioned in the question; in this example you could apply one mode of Christian ethics to the environment, and/or a more contemporary approach like 'deep ecology'. Your last paragraph should be a conclusion, where you sum up your essay's argument in relation to the question (is utilitarianism the best approach?) concisely and present some final thoughts.