The overused nature of the expression usually confirms that it is a cliche. For example, when one hears a politician say, "We are going to study the problem," or an athlete say, "We are going to take it one game at a time," these expressions might be valid but they have been so overused that merely hearing them causes the listener to tune out to a certain extent. Popular dialogues might be seen as popular because they have not been overused. Over time, they might be overused, making them cliche. For example, "Where's the beef?" was a popular expression in the 1984. When it was used in a Presidential Debate in 1984, its zenith was reached. Afterwards, it was featured in many more commercials. Over time, when it was used, it almost seemed bland in the fact that the cliche nature had been revealed in that it had been overused. In this example, a popular dialogue ended up becoming cliche. Clara Peller's statement might be a good example of a cliche that can emerge from popular lexicon.
The best definition that I know of for a cliche is that a cliche is a trite phrase. That means that it is one that has been used so much that it is in fact overused. So, typically, a cliche is a phrase that you have heard over and over to the point where it is not at all fresh.
Some cliches might be "pretty as a picture" or "it's a piece of cake."
This means that the only way to identify cliches is to know what phrases are overused. You cannot identify a cliche in any other way. You just have to know what phrases are overused in your country -- those are cliches.
Cliches can be phrases, quotes, proverbs or any other often used expressions. In general cliches represent some of the best of such expressions, but which have been used so much that there is no novelty left in their use.
When a person comes across for the first time an expression that has moved in the class of cliches by its over use, the person has no way of knowing this. The only way a person can classify an expression as a cliche or otherwise is on the basis of how often he or she has come across the expression. Thus, classification of a cliche is very much a matter of personal experience, judgment and preferences.