Clichés are phrases that have been overused to the point that they are no longer interesting. They are predictable to a fault, these phrases convey very little actual meaning. For example, here is a list of cliches. Cover one side of the phrase with your hand and see how many of them you don't know.
selling like hot cakes
blind as a bat
butterflies in your stomach
cool as a cucumber
sly as a fox
like pulling teeth
Some cliches are ambiguous or vague while others simply become outdated.
Bark vs. Bite
"Its bark is worse than its bite"
Wouldn't any bite be bad? What if the bark is REALLY bad?
The best way to use a cliche is not to use it at all. If you feel as though you need to use a cliche, try to twist it into something new or unexpected. Don't stretch the language too far, but you can put a new spin on an old phrase. Even flip flopping the word order can make a difference: "don't be fooled, its bite is definitely worse than its bark"
So how does a reader view a cliche? Because they are such predictable phrases, the reader is likely to think that the writer didn't make the effort to be original or creative. Too many cliches and you might lose your reader all together.