How do I know what an essay question is asking and what the examiner is looking for in an answer?

With essay questions what I usually did was underline what I thought were the key words. For example:How does Shakespeare portray love in sonnet 116? For this question I would underline the words: how, portray and love. With each underlined word I would then go through and define each one. When the question asks "how" begin to think about the techniques which Shakespeare employs which often can be answered through his use of language, structure and form. Then with the word "portray" is when you would begin answering what Shakespeare is trying to achieve through his "how" methods which you previously identified; what does his personifiaction of Time for example tell you about (or how do you interpret) what image he is displaying of love? Finally the word "love" would simply hone your answer and channel you into the subject matter so that you dont end up simply writing a general critical analysis.