A Shakespearean sonnet is a type of 14-line poem that is written with the same structure that Shakespeare uses for his sonnets. They are written predomenantly with a rhythm scheme called iambic pentameter, in which each line is ten syllables long. In order to discuss analysing Shakespearean sonnets, I will use an example of this poetical structure: John Keats' "When I Have Fears That I May Cease to Be". Keats wrote this poem after intensely studying Shakespeare's poetical works, and thus closely imitates much of his techniques.
First of all, print the poem off the internet and make it a large font with large line spacing. Then, take a different coloured pen for annotation. The key thing to do when analysing these sonnets is to note the structure, and how the structure compliments the subject matter, and vice versa. For example, sonnets are primarily used by poets to express love or desire, but in some cases this undertone is juxtaposed by what the poet is trying to say. In this case, Keats is using the love-poem structure to emphasise his own mutability in contrast with the abundance of literature he has yet to write.
Once you have analysed structure, (eg. written down the rhyme scheme next to the lines, noted the 14 lines, studied the iambic pentameter, thought about the relevance of the 'love poem' structure) you can now begin to analyse how the structure contributes to your interpretation the poem's overall meaning. "When I Have Fears That I May Cease To Be" is in fact all one sentence - only the very last line is end-stopped. This suggests Keats' unfulfilling and worrisome rambling thought about losing his affinity with the world. The whole poem conveys his ambiguous attitude to death - on one hand, it seems a waste and a tragedy - but on the other, he seems to suggest that it would be a form of escapist relief. Keats' use of the word "when" to begin the poem suggests that his fears about death consistently plague him. The final two lines of the poem are a rhyming couplet, emphasising the finality of death that Keats so fears.
The next step in analysing the sonnet is to have a look at the language. Keep an eye out for internal rhyme, metaphors, use of adjectives, symbolism, who the poet is addressing and cross-literary references. Write all your thoughts about the poem down underneath it. One point to note about this poem is how Keats' personification of nature combats conventional religious ideas of an afterlife, implying that all that awaits us is oblivion. For the Romantic poets, Christianity destroyed the naive visionary power of a mythic relation to nature, and thus Keats purposely omits any Christian references from his poem.
The final step for an A-Level student is to research critical perspectives. Have a look on websites such as Google Scholar, or visit an academic library.