How would you advise approaching an unseen piece of poetry or prose in an exam?

You should read the poem through first without annotating or writing anything down in order to try and absorb what the poem means as much as possible. On the second read through, it is really useful to annotate the poem as much as possible. Even if your thoughts seem trivial or you think you may be wrong, write down any initial thoughts that come to mind, regarding any element of the poem. Try and keep it neat so you don't obscure the poem, as you will need to keep referring back to it. If you have any ideas for paragraphs based on a specific theme, note the theme down. Preferably read the poem a total of three times before you begin to write your response. Remember, the time for formulation of ideas is integral so don't rush it. 

When annotating the poem you should be looking for a variety of different things. How is the poem structured, how many stanzas are there, are they all the same length? What is the metre of the poem, is it iambic pentameter (ten syllable lines, alternating unstressed then stressed), or is it completely irregular, is there anywhere in the poem which breaks from the prevalent metre? What is the tone of the poem, satirical/elegiac/euphoric? Are there any literary features such as metaphors/similies/alliteration/assosance/sibilance/enjambment/personification, what are the effects of these features? What does the title tell you? Is there a rhyme scheme, what is it and how does it effect the poem? Is there any interesting words, why do they stand? Think about as many of these things as possible in your answer.