Personification attributes the characteristics of a person to an inanimate object. They key to success is to make the comparison surprising but appropriate. Charles Reznikoff's poem is a good example:
Permit me to warn you
against this automobile rushing to embrace you
with outstretched fender.
The poem makes us chuckle because cars do not embrace people or try to shake hands. However, the comparison feels right because cars can approach as suddenly and unexpectedly as strangers.
Personification does not have to be humorous. Consider Philip Larkin's poem, "Aubade":
Meanwhile telephones crouch, getting ready to ring
In locked-up offices.
Here the crouching phones seem sinister, as if they are waiting to attack.
A metaphor compares two unlike things, forcing the reader to make a connection between them. This kind of comparison does not use "like" or "as." The key to a great metaphor is balancing surprise with the shock of recognition. For example, Charles Reznikoff writes:
Walk about the subway station
in a grove of steel pillars
Here the subway is compared to a forest, forcing the reader to think about the difference, or lack of difference, between the human and natural world.
A simile is a special type of metaphor that does use "like" or "as" to make the comparison explicit. For example, in "Aubade," Philip Larkin writes: "The sky is white as clay, with no sun." Here Larkin forces the reader to compare the sky with its opposite, the earth.
An extended metaphor is when a poem explores a single metaphor, or simile, in great detail. The poem "April" by Alicia Ostriker is a great example:
... What a concerto
of good stinks said the dog
trotting along Riverside Drive
in the early spring afternoon
sniffing this way and that
how gratifying the cellos of the river
the tubas of the traffic
the trombones
of the leafing elms with the legato ...
Symbols are objects or people that stand for abstract ideas. The connection is made either through shared characteristics or the repeated association of a thing with the idea it represents. The key to success is to avoid the obvious or cliché. For example, the idea that love is like a rose is so overused that it has lost its original force. Beyond avoiding cliches, nearly any object can be linked with any idea.
One example of a symbol is in Wallace Stevens' poem, "The Man With the Blue Guitar." Throughout the poem, the blue guitar becomes a symbol for the imagination.
Allegory is a special type of symbolism. This is when an abstract idea is made into a character in a story. For example, in Edmund Spenser's long poem, "The Fairie Queene," the main character is named The Redcrosse Knight. Both his name and his armor show that he represents Christianity.
Metonymy and synedoche are both forms of substitution. Metonymy is like a nickname; instead of referring to the thing directly, this figure of speech uses a related word. One example would be referring to your tall friend as Tree. Synedoche uses just part of the thing to refer to the whole thing. An example might be referring to your tall friend as Bigfoot. Both figures make the expression vivid and interesting. The key to success is choosing an appropriate way to refer to the object. For example, in the famous poem, "Elegy Written in a Country Churchyard," Thomas Gray writes "drowsy tinklings lull the distant folds." Here the poet refers to sheep by the sound their bells make, an example of metonymy that allows us to hear the bells clearly.
Hyperbole is deliberate exaggeration to the point that the idea becomes ridiculous. Understatement is the opposite; the idea is downplayed to the point that it becomes ridiculous. Both are frequently used for humorous effects. The key to success lies in making them both obvious and absurd.
Remember that language has to go beyond its real-world meaning to be figurative. Alliteration and onomatopoeia are sometimes listed as types of figurative language, but these are really sound effects that can be figurative or not. Many print and online sources exist to help you practice identifying and using figurative language.