One of contraints in composing Chinese couplet is the writing style. The two sentence should be indentical in their writing styles. For instance, if there is a repetition of words, characters, or pronunciations in the first sentence, the second sentence should contain an identical repetition. And if  there is a character decomposition in the first sentence, i.e., the first sentence contains a character and its "component characters", the second sentence should contain a character decomposition at the corresponding position.

Some Chinese characters can be decomposed into other characters. For example, "好" (good) can be decomposed into "女" (daughter) and "子" (son). The left part of "好" is "女" and the right part is "子". "女" and "子" are called the "component characters" of "好".

Compare to wester couplets, which also consist of two sentences that usually rhyme and have the same number of syllables, Chinese couplets have much stronger constrants. Because in Chinese each character has one and only one syllable, the same number of syllable means the same number of characters. Moreover, the constraints of the first sentense and second sentence on consistency of part of speech sequence and writing style make Chinese couplets have more regular form.

The following example shows the repetition and decomposition techneques used in making a perfect Chinese couplet.

有女有子方称好
have daughter have son so call good
缺鱼缺羊敢叫鲜
lack fish lack mutton dare call delicious

This couplet means: Once one has a daughter and son, one's life is complete; who would dare call a meal without fish and mutton delicious?

The first Sentence contains a repeated character “有”(have), and a character decomposition: “好”(good) and its "component characters" "女" (daughter) and "子"(son). So it requires that the qualified second sentence should contain identical character repetition and character decomposition.

A perfect second sentence has been worked out after multiple attempts by many people for this first sentence. 
In this example, the second sentence equally contains a repeated character "缺" (lack), and a character decomposion: "鲜" (fresh) and its "component characters" "鱼"(fish) and “羊” (mutton) at the correspoding positions. And the meanings of the two sentences are also parallel: they tell us what is important in life and what is important in cuisine, respectively.