A metaphor is a figure of speech comparing two different subjects to emphasize a trait they have in common. These subjects can be objects, people, animals, colors, concepts, phenomena, etc. Some examples of metaphors are
"the lake was glass,"
"her words dripped with honey,"
"a fish scaled in gems," and
"the river of life."
Be careful that you don't confuse metaphor with simile, for though they are similar, a metaphor does NOT use the words like or as.
Also, avoid combining unrelated metaphors, which creates a confusing expression known as a mixed metaphor. An example of a mixed metaphor is something like, "An ace in the hole shouldn't be put on the back burner." This is a problem because the author tries to combine metaphors of poker and cooking, which invokes imagery that is too incongruent.