It is never a nice situation when someone owes you money. First off, you need to remember to be friendly but professional. Use your accounting software to review your receivables at least once a week. Then develop a system for following up with payments that are three days, one week, 15 days, 30 days and 45 days late. Start by sending a reminder letter. Next, make a phone call. Remember not to threaten or get angry. If you still don’t get a response, then consider taking legal action or using a collection agency.