Before You Start Writing
It can be daunting to have to critically analyse a poem you've never seen before, especially if you're under exam conditions. It is important however that you do not panic, even if you've read through the poem once and have no idea what the poet is talking about. Read through the whole poem slowly a few times, try and pick out the key themes of the poem (It may be helpful to use a highlighter here). What is the poet attempting to communicate? What sort of language do they use? Is it happy, sad, descripitive, vague? Are there any parts that stand out to you? If so why? What techniques are being used and what is their effect? Even if after you've done this there are still some parts you don't understand, don't worry, focus on the bits that you do understand when writing your answer and leave out the bits that you don't.
Writing Your Answer
Start off with an introduction, outline what you think the poem is about and what the poet is attempting to communicate. The introduction doesn't need to be long, if you're answering a specific question on the poem you should make reference to the question you are being asked.
Then you need to get into the body of your answer, many people find it helpful to use the P.E.E.D. structure for this section, This stands for 'Point, Evidence, Explain, Develop'. First, make your point, what are you saying about the poem. Then give your evidence for why you think your point is valid, the evidence should be taken from the poem, a technique or choice of language that the poet has used. Then explain this, how does the evidence support your intitial point. Finally, develop, can you relate your point to the wider poem? Do we see the poet do something similar anywhere else in the poem? Try and tie each point you make into the next point so that your answer flows together.
Finally, you need to conclude your answer, try to sum up all of the points you've made. Your conclusion will often be similar to your introduction as you give an overview of the poem and the key themes. Come to a final conclusion about what the poem and poet is communicating.