A metaphor is similar to a simile in that they both make comparisons. However, a metaphor goes a step further and says that one thing actually is another thing. Metaphors help to explain concepts and ideas by making links.
Metaphors work well when they make more than one connection. If you use a metaphor within your work, try to make more than one comparison; flesh out the idea so that the reader gets a strong picture in their mind.
Listening to this video will help you to understand the differences between a metaphor and a simile. It also discusses how metaphors can become cliches. In your work, try to avoid cliches and instead use your creativity to make unique metaphors.