Read through it a couple of times and write down your first impressions. If you're able to integrate your personal response into the essay that's always something they like. For your opening paragraph, talk about the obvious things: is there a rhyme scheme, or any sort of metre? Does it follow a specific form (like a sonnet, for example)? What perspective is it from (eg if it's from a 3rd person perspective, you could make the point that the writer is creating distance between the reader and the characters in the poem)?
Then go into your analysis, making sure you answer the question. If the question asks how the writer presents something in the poem, try to find 3 different ways the writer presents that particular thing. Look out for techniques such as enjambment (which can speed up the pace, building tension, for example), or caesura (a pause in the middle of the line, which can slow the pace, or emphasise something important). Those are good structural points to make.
In terms of language, try to find metaphors and similes, alliteration, symbolism etc and look for the deeper meaning behind it all. Also, use of pronouns - if there is any use of second person, that suggests direct address to the reader/listener and you may be able to make a perceptive point out of that.
If you think the point you're making might be a bit of a stretch, maybe consider making a different point, but if you're really set on it, use tentative language ('perhaps' is always a good one, as it makes you sound more sophisticated!).
Finally, for your conclusion, you basically need almost an outline of your essay, and see if you can make any points on the 'bigger picture' - you spent the whole essay looking at the small details of the poem, the menutii of how the author has presented an idea or a character - now look at the overall message. What has the writer been trying to convey/tell us?
It's a lot to write in not very much time, so remember that unseen poetry is only worth 20 marks. I wouldn't advise spending more than 35 minutes on it, because the other question is worth 45 marks, and should really be your priority. Maybe the way to do it is to look at it as bonus marks: the main task is to write about your text (OMAM, TKAM, whatever), and these marks are what might push you into the grade above.
So don't sweat unseen poetry too much - it's not that important. I've got my exam tomorrow too, and I've been dreading it, but working out a technique like that has been an absolute lifesaver!!