Metaphors and similes are both figures of speech (a way of writing!) used to create imagery in the mind of the reader.
A simile makes a direct comparison in an attempt to make the description more powerful.
Notice these are both introduced with ‘as’ and there’s another ‘as’ soon after.
Similes are used extensively in poetry. According to Bartleby.com Shakespeare had 559 of them, many of which include the keyword ‘like’.
So: ‘as’ and ‘like’ can signal a simile.
A metaphor makes an implied comparison between two things – without using ‘as’ or ‘like’ for flag it up for the reader. Here are a couple of examples.
These are good uses of metaphor. In a poetic form of writing, as in a song or a play, where brevity is essential, metaphors conjure an image in a few words.
Writing’s hard work? Who can blame writers for wanting to put their feet up occasionally?
Your characters might use metaphors and similes within dialogue (or thoughts), but if you also use them in exposition, you are robbing the reader of coming to his/her own conclusions about what’s going on, and how your characters are behaving. You are wandering into the realms of ‘telling’ instead of ‘showing’. Tut, tut!
The greatest sin – apparently – is mixing your metaphors: combining two unrelated metaphors and thoroughly confusing the reader. Or making them laugh.
However, a writer might choose to combine metaphors to illustrate a point. Consider this extract from Lynne Truss and her famous book on punctuation: Eats, Shoots & Leaves
Well, if punctuation is the stitching of language, language comes apart, obviously, and all the buttons fall off. If punctuation provides the traffic signals, words bang into each other and everyone ends up in Minehead. If one can bear for a moment to think of punctuation marks as those invisibly beneficent fairies (I’m sorry), our poor deprived language goes parched and pillowless to bed. And if you take the courtesy analogy, a sentence no longer holds the door open for you to walk in, but drops it on your face as you approach.