There are few, if any, hard and fast rules for writing poetry. It is a subjective art form that affords its authors freedom to express themselves in ways both traditional and innovative. Poems do not have to rhyme, nor do they have to follow any particular structure or include any particular style. Still, most poems do feature a few key characteristics. These are stylistic choices that can vary from piece to piece, but must nonetheless be made by every poet.
Figures of Speech
Figures of speech, or figurative language, are ways of describing or explaining things in a non-literal or non-traditional way. For example, a metaphor describes something by likening it to something else: "His touch was a lightning strike." The author doesn't mean that the touch was literally a lightning strike, but rather that it produced feelings of heightened excitement and charged emotions. Other figures of speech may include hyperbole, which is a frequently humorous exaggeration that hints at a larger truth. The quote "I ran faster than a cheetah" is an example of hyperbole. The mention of object to symbolize or represent something else is also hyperbole.
Imagery is something concrete, like a sight, smell or taste. Imagery describes what the poet sees, hears or otherwise senses, be it a literal image or one that exists in his mind. Visual imagery, which describes what the poet sees, is the most common type of image in poetry. It creates a picture that the reader or listener can see in his mind.
Punctuation and Format
The punctuation and format of the poem deal with how it is arranged on the page and how the author intends for you to read it. For example, if a poem has frequent line breaks and short stanzas, it forces you to read it in a different rhythm than if it were arranged in longer stanzas with fewer breaks. To better understand this concept, read poetry aloud instead of in your head; when you read poetry, or listen to the poet read his own work, you see the impact of the format.
Sound and Tone
Poets use different sounds and tones throughout poetry to change the way it sounds. For example, the poet may use alliteration, which is when multiple consecutive words start with the same letter. For example, he may write, "Pretty pugs playfully prance on the promenade." The poet may choose his letters to give the poem a soft or sharp sound, as well. For example, choosing words that use "soft" consonants like f, m and w produces a different sound than words with "hard" consonants like d, k, t and z.
Choice of Meter
The meter of a poem is the rhythm or pattern of speech with which you read it, and it doesn't happen by accident. Poets use different meters to give their poetry different rhythms, which have technical names like iambic pentameter or spondaic heptameter. These names function like measurements for poetry -- a poem's rhythm and meter can be broken down and analyzed according to measurements like these.