How do I write about poetic meter in an essay?

Poetic meter often supports the meaning and/or tone of a poem. In an essay, it is important to not only describe the metrical structure of a poem, but also to explain how this impacts the poem as a whole.

The metrical structure of a poem will often reflect its meaning. For example, Percy Shelley's 'Mutability' is written in regular iambic pentameter, the most popular metrical structure in English poetry:

"We are as clouds that veil the midnight moon"

The unflinching regularity of this poem is perhaps suprising when we consider that this is a poem about change. However, Shelley writes about the constance of change, how the only thing that isn't mutable is mutability itself; you could then write that the regularity of the poem's iambic pentameter reflects this contradiction central to the poem's meaning. 

Another example is how meter effects how a poem sounds and determines its tone. For example, Tennyson's 'The Charge of the Light Brigade' has a dactylic dimeter: 

"Half a league, half a league,/ Half a league onward"

The meter makes an audible impression of the charge forwards, and this sound creates an urgent tone, allowing the reader to imagine themself in the midst of the battle; this demonstrates how important meter is to the impact of a poem.