A good song is like poetry put to music, making it more difficult to analyse than some people might think. A song is full of literary devices and figurative language, and music adds another layer of meaning. When writing an essay about a song, you can't pay attention to the lyrics alone. The melody played along with the words can modify the meaning, since the language of music can also deliver a message.
Listen to the song a few times. Without thinking too much about stylistic specifics yet, write down how the song affects you. Decide how it makes you feel, and try to discern a central theme or message.
Get a printout of the song lyrics so you can scrutinise them more closely. Scour the words for literary devices, and consider how their use affects the meaning and feel of the song. For example, consonance (repetition of consonant sounds, especially after a stressed vowel) can make a line of poetry sound harsher to the ear. A songwriter might use it in a song lyric to communicate frustration over a recent break-up.
Listen to the song again with your list of lyric observations in front of you. Consider how the music lines up with the words. Cock your ears for crescendos, pauses, instruments fading in or out of the arrangement and tempo changes. Ask yourself how these details enrich the meaning of the lyrics and contribute to the effects of poetic devices. Add to your sheet of notes.
Research the historical, social and political context of the song. Music is often reflective of life experience, so knowledge of world events and prevailing attitudes might affect your interpretation. For example, some people think that Don McLean's "American Pie" is a commentary on changes to American culture at the time.
Study the song within the context of the entire album. Ask yourself whether the album has a theme, and how the song you've chosen to analyse contributes to its overall feel. Look at the order of the tunes; decide if the artist chose a deliberate progression of songs to convey a message.
Examine the observations you've gathered and look for a common thread that ties them together. Link your detailed observations to your general impression of the song. Your conclusion about the song will be the thesis for your essay. Choose which specific examples you'll use to support your argument. It's OK to leave some out to limit the length of your paper.
Draft your paper, using the regular conventions of essay writing and considering any special instructions from your teacher. State your thesis and briefly outline your main arguments in the introduction. Devote the body of your essay to expanding your supporting points. Restate your argument and summarise what your paper discussed in the conclusion. Edit your paper for spelling, grammar and clarity. Have someone else read your essay and provide constructive criticism before writing a final draft.