The main rules are that it must be related to the name, and the second is the word limit, which can generally be a single word or a double word, no more than two words, and there are no other special requirements.
In ancient times, it was inconvenient to call a man by his first name when he was twenty and a woman was fifteen. Therefore, another alias related to the meaning of the original name was chosen and called a word to express its virtue. When ordinary people call each other respectfully, they must call them the words that express virtue, and then call the words "Piaozi". For example, Li Bai's characters are too white and he often uses characters as lines.
A character usually has one or two characters. The most are two words. The character limit is mainly for the convenience of others to address you. In ancient times, due to the special emphasis on etiquette, the names and characters were very particular. In interpersonal communication, first names are generally used as modesty, condescension, or as a term of address for superiors versus inferiors, or for seniors versus juniors.
People of the same generation only call each other by their first names when they are very familiar with each other. In most cases, it is considered impolite to refer to each other or call others by their first names. It is considered polite among peers to address each other by name.
Extended information:
How the meanings of words and names are related
1. Parallel expression. If the meaning is the same, that is, the character and the name have the same meaning and are connected, and they are in a parallel relationship, so they are also called "parallel formulas", such as Qu Ping, the original character. Guangping said Yuan, meaning the same.
2. Auxiliary. Those with similar meanings, that is, the words and names have similar meanings but are not exactly the same. They can assist each other and are called "auxiliary forms". For example: Liang Hong, named Boluan. Luan and Hong are both birds, but they are not the same species. Hongyan and Luanfeng can help each other.
3. Contradiction. If the meaning is opposite, that is, the meaning of the character and the name are opposite, this situation can be called a "contradiction", such as: Zhu Xi, the character is obscure. Xi is the dawn, Hui is the night.
4. Expanded. The meanings are consistent, that is, the word and the name often come from a sentence, the meanings are consistent, and the word supplements or modifies the meaning of the name. This situation can be called "expanded". For example: Xu Qian, with a long character. "Kong Congzi" said: "It is not that the body is great." The name and the character have the same meaning in one sentence, and the character provides a supplementary explanation to the name.
5. Extended type. The meanings are extended, that is, the meaning of the word is an extension of the meaning of the name. This situation can be called "extension". For example: Li Bai, whose courtesy name is Taibai. Taibai refers to Taibai Venus, which is an extension of the meaning of dialogue.
Reference source: Baidu Encyclopedia-Biaozi