Such figurative language is more than decoration; it creates a special meaning or understanding because it strays from literal meaning. It uses words in a connotative sense for the associations, nuances, and suggestions they evoke in a listener's mind. Metaphor and simile are generally concrete and sensory, linking to experience, to life lived and felt. Using them is a matter of style, the means by which one speaker or writer persuades an audience.
And while figurative language is not the only component of style, it's important in helping the speaker build pathos, an appeal to emotion.
These two figures of speech compare two things that are not alike, the metaphor doing so by saying one thing is the other (the heart is a pump) and the simile by saying one thing is like another (the heart is like a pump). Thus the first thing takes on the attributes of the second.
Similes and metaphors can be descriptive techniques, but they can also help change or create a perspective. They generate new thoughts and ideas. They can rouse interest and curiosity, produce understanding and empathy, provoke anger or disgust, awaken joy or sorrow, restore ease or establish an association. We have emotional attachments to places, things, ideas, people, and concepts that the terms of a simile or metaphor often touch. Appeal to those attachments.
How do you find and form similes and metaphors? You've been using them almost since you began to speak and probably use them daily in ordinary conversation. Let them become a part of presentations as well. When you are preparing, consciously look for content that lends itself to a comparison. Then apply your experience to it, things you have done or read or watched or studied.
Perhaps an article you've read about bowerbirds sparks a metaphor between a process you support and the birds' nest-building habits. Or maybe you see a similarity between hazards you want to discuss and the crocodiles that lie in wait for wildebeest during the Great Migration.
Or start with a feeling you want to appeal to—fear, trust, satisfaction—and work toward a comparison that touches it. Beginning a new endeavor, for example, might be compared to a child's attempt to climb a tree, to his fear of the task, his trust that he can accomplish it, his resulting satisfaction.
You can also force similes and metaphors. To do so, jot down the first term—an idea or point you intend to discuss. For the second term, choose a category, bodies of water or kitchen gadgets, for example. List things that fit into the category—river, lake, lagoon; blender, frying pan, serrated knife. Then compare the first term to the items on your list. You'll find an apt comparison.
The brilliance of figurative language is that creating it will change your thinking, too. You'll become more aware of the role of emotion in persuasion and of ways to use words to connect with your listeners and to clarify your messages. Those messages will be more memorable, too. What was it that the fictional Dr. House said about the liver?