"The most essential gift for a good writer," said Ernest Hemingway, "is a built-in shock-proof shit detector."
How true. Though usually we have to grow one rather than having it built in. My own acquired detector is always on the look-out for cliches. There are so many time-worn phrases that don't even feel like cliches, that we are easily tricked into using them.
The boon of the cliche is its instant recognizable signal. It does what it says on the tin. (Oops, there it is.) But this is also its liability. It's too recognizable. It doesn't surprise the reader, and thus doesn't hook him into your prose. Finding another way to say it, one that is uniquely your way, is key to finding your voice.
It's not just another way of saying how blue the sky is, how her heart pounded or announcing the effect of shock. It's looking for a completely different angle on the subject ('thinking outside the box').
Why talk about the sky at all? Why not concentrate on light and shadow, for example, and its effect on the surroundings. For that matter, why not take shock out into the environment and examine what the shocked person sees and how it changes in their consciousness? Instead of pounding hearts, what about the heightened sense of sound outside the body?
It can be more effective to do the opposite of what is going on. If the situation is interior with the person, go outside for your effects. If the situation is exterior, go inside and show their reaction.
This is only one way of avoiding cliche. There are as many ways as there are writers. The key is first to start noticing the cliches in your work, and then backtrack and think how you could express this almost using another dimension. Surprisingly, once you have forced yourself through it for a while, the practice becomes part of your craft and it isn't nearly as difficult to do as you might think.
And when you read, look at how other writers do it. At the least, it'll hone your shit-detector as you start noticing the cliches they missed.