For unseen poetry, you should always read through the poem at least two or three times in order to understand the content and pick out which features you'll analyse in your answer. On your first read, focus on just that! Read the whole poem and try to get a sense of what the message is. Focus on any features that immediately stand out to you on your second read through, such as the rhyme scheme, metre or use of imagery. You can then highlight instances of these key features and think about what effect they have. For example, if the poem is a ballad, does this relate to its content or contrast it? Do this for each feature you want to write about and make a brief plan for your essay before you begin writing. This is important as it will allow you to keep track of your points and make the best use of the time you are allowed.