Dear (Mrs./Mr./Miss/Ms.) followed by last name,
In your introductory paragraph, briefly summarize the reason for your collection letter.
The main body of your letter should contain all details regarding the debt you are attempting to collect. If the letter is to a tenant, explain that they owe x amount of dollars and how many days past due they are. If you are writing to a consumer who is past due on payments, give all details such as account number, due date, policy number, and the last day for payment before the recipient may be turned over to a collection agency. Also explain that this may affect their credit rating.
Your last sentence should urge the recipient to take action immediately, so they can avoid possible damage to their credit or further action. Reiterate the deadline, so that there is no mistake about when you expect payment.
Sign your name above the typed signature. Make a copy of the collection letter before you send it out. You may also want to consider sending your letter via certified mail, so that you know for certain the recipient received it.