Metaphor is one of those things that is rarely explored in any depth in a classroom — even in creative writing classes, but should be. A successful metaphor is a figure of speech that lifts an everyday object or observation off the page and makes the reader pay attention, but does so without disrupting the fictive trance (I’ve never read anything about this, but my guess is that when you’re deep into reading and the story is working, you’ve entered a light hypnotic state; that’s what a writer hopes to bring about in a reader).

A clumsy metaphor is like a slap in the face (that’s a simile, of course). Even a cliche (and most cliches are metaphors) is preferable to a bad metaphor; cliches register as nothing at all.

Before going any further, it’s probably a good idea to have a look at this website by Ronnie Manalo Ruiz which summarizes the various types of metaphor. With those distinctions in mind, if you start paying attention to metaphor in your fiction reading, you’ll notice how prevalent they are.

The simplest way to look at a straight-forward metaphor is A=B. This applies to simile as well, of course. I’m going to use some less than wonderful metaphors [note addition (thanks, Ed): and similies] to demonstrate and hope you won’t find it necessary to shoot the messenger. In these examples the first term in parenthesis is A, the second, B.

(you) are the (wind beneath my wings)
his (eyes) were like (three-minute eggs)
the falling (snow) made a (blanket) over the world

By these examples it should be clear that A and B are distinct objects being compared to each other because they share some crucial characteristic, for example: your influence on me is such that I am motivated to strive for greater things; or, his eyes were disgustingly runny; or, the snow made the world seem peaceful and comfortable.It must be said that writing about romantic relationships and strong attachments produces some of the most awkward metaphors, maybe because it’s just hard to write about the mania that goes along with falling in love, or lust. Which brings me to the next point.One mistake novice writers seem to make a lot, in my experience, is stretching so hard for the right metaphor that they forget whose POV they are writing from. The way one character perceives Sam’s smile will be (should be) distinct from the way the next character sees that same smile. To his little sister, his smile might be (forgive me, I’m making a point) a ray of sunshine while his landlady sees it as sputtering neon. The metaphor webpage I’ve referred you to puts the point very clearly:

a metaphor provides…a cue to what kind of thinking should be done…Metaphors act as a shepherds to lead the audience onto the correct path of thought and mindset.

And now the exception to go with the rule: you must avoid over-extended, awkward, cliched metaphors at all costs, but your characters have no such restrictions on them. A character can get away with an awful metaphor, if it’s handled well. A character who tells everybody he works for the CIA but secretly writes Hallmark cards for a living might find himself blurting out aren’t you just a ray of sunshine! when he’s nervous. A mother at her wit’s end with a difficult teenager who buys every self-help parenting book on the market might spit out one cliche after another when her daughter comes in at three a.m. She can get away with it; you can’t. When that same mother goes into her daughter’s room an hour later and studies the girl’s sleeping face, what she sees there — what you let us see through her eyes — has to be simple and clean and honest.