1. Before writing the IOU, be sure to find a clean and tidy piece of paper. The paper size is not limited, but it must be complete. Because there have been disputes between borrowers because of incomplete paper, everyone must choose and keep it carefully. 2. State the basic information of the borrower and lender, such as name, ID number, etc. 3 clearly state the borrower's borrowing reason, borrowing time, repayment time, repayment method, interest calculation and overdue repayment solution. 4. It is best to have witnesses or guarantors when signing the IOU, and write down their basic information on the IOU.