How do I effectively comment on the formal features of a poem?

The one thing to remember is that if you're commenting on the formal features of a poem, make sure it adds to your argument. Don't just spot devices for the sake of it; comment on how the use of rhyme (or anything) adds to the overall effect of the poem.For example, in Hopkins's 'The Windhover', the use of alliteration is prominent throughout, giving the poem a sense of control and making it sound musical. Always give an example of this - quote a strong example of whatever device you're commenting on, and then say how it's effective. In Hopkins's poem, the line '-dom of daylight's dauphin, dapple-dawn-drawn Falcon, in his riding' is dominated by alliteration of the 'd' sound, emphasising each word and perhaps reflecting the speaker's wonder at the bird he has just caught.