First, a proviso... it is easy to get carried away with the magic of language and 'write over our heads'. The first business of writing is to be clear about meaning. Meaning, sense and clarity is our primary activity. Tom Bailey, in his excellent book 'On Writing Short Stories' (in the library), puts it like this:
Voice, Tone, Mood
Meaning, Sense, Clarity
This is a pyramid and you must deal with the bottom layers first.
i.e. unless you get the meaning, sense and clarity down, then the 'higher' stuff has no foundation and the reader will fall into a hole of incomprehension (and therefore boredom). Bailey talks about the 'loose reader' who is able to make the most fantastic cathedrals in the air out of the smallest slips of the author.
Having said that, metaphor and figurative language (simile, symbol) is the writer's muscle, making writing work double time. Similes use 'like' or 'as' eg. 'she looked bloated, like a body long submerged in motionless water.' The comparison should enlarge our understanding - don't just add one because the rhythm of the sentence demands it.
A metaphor echoes a larger truth. It is the thing being compared to, rather than being like it. Fabulous example is Updike's picture of the Colosseum as a ruined wedding cake. The best metaphors are born naturally out of the story, do the hard work of capturing character first and then go back and examine what's there, what images and symbols you can add too and refine. I wrote a story once called 'Green' because the girls in it are naive, but it expanded to include all aspect of green-ness (jealousy, money, the green sea, they had an avocado bathroom...) Think about 'families' of symbols or metaphors - shapes (a snake, a curly hair).
A symbol is a object or sign which carries its own weight of meaning, like the blue-eyed doll in this story by Robert Boswell.
Another example is Raymond Carver's Gazebo (the title of the story and also a symbol for marriage). Watch out reading Carver, there's never a bird sitting on a telephone wire without a reason!