Legal analysis: first write in block letters, with the signature of the parties, indicating the date and place, preferably with handprints and witnesses.

Two, the agreed affairs do not violate national laws and regulations or public order and good customs.

3. The agreed affairs shall not harm the rights and interests of the third party.

Fourth, it is better to be fair.

Legal basis: Article 143 of the Civil Law of People's Republic of China (PRC) A civil juristic act that meets the following conditions is valid:

(1) The actor has corresponding capacity for civil conduct;

(2) the meaning is true;

(three) does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.