Summarize the following:
If your initial agreement didn't have a strict due date, then you will have to make that determination on your own. Decide how much you trust the person to pay without you directly asking.  Take the amount owed into consideration. A small debt may not be worth pursuing right away, while a larger debt might take some time to collect. If you are owed money in the course of a business transaction, ask for it as soon as possible. Waiting on the debt will only make it harder to collect. Once you have passed that date, make a request for the money. At this stage, all you want to do is make sure that the debtor is aware that their debt hasn’t been paid. Sometimes people just forget, and a friendly reminder is all they need. More formally, this is called an "inquiry contact."  Don't demand payment, instead offer a reminder ("Do you remember the money you owe me?") that allows the debtor to save face. Include all relevant information when asking about the debt. You should be prepared to provide the amount given, when you received the last payment, the amount owed, any payment arrangements you are willing to accept, contact information for you, and a clear due date. If you are dealing with a company or client, it can be helpful to make this inquiry in the form of a letter. This gives you a paper trail if the situation escalates. For a due date, 10 to 20 days from the date the debtor receives a letter can be a good timeframe. It is in the foreseeable future but not close enough that the debtor feels panicked. It may not be worth it to you to wait for the full amount. If the amount is small, or you do not believe the person will be able to pay, consider letting them provide something else in return. Providing a service or other favors will work if that arrangement is acceptable to you. If this is the case, be clear about the offer and collect as quickly as possible. Don't be too quick to bargain, as this may send the message that the debt can be negotiated down, or that the debtor can take even more time. These are called "demand contacts." If the debtor does not respond to your request, you should be more direct. Make sure it is clear that you expect immediate payment or a definite commitment to payment, and provide clear instructions for making that payment.  Your language here should be more direct, and show some urgency. Phrases like "You need to pay now," or "We need to come to an arrangement now" let the debtor know you are serious, and you are not willing to negotiate further. Include clear consequences for not paying. Let the debtor know what you plan to do if you do not receive proper payment on time, and be prepared to follow through. If you don't receive any payment resulting from the demand contact, then chances are that the debtor either doesn’t have the money or just doesn't feel like paying. It’s your job to make them prioritize you through multiple contacts by phone, letter, e-mail, or in person, so that they decide to pay you before they pay someone else (or head for the hills). Hiring a third party to conduct your claim lets the debtor know you are serious, and can free you up from the hassle of contact and arranging payment. Collection agencies will charge as much as 50% of the payment for their services, so you need to decide if the partial payment is better than nothing. If the payment for a collection agency is too steep, you may consider skipping this step, and going to small claims court. If you are collecting your own debts, there are certain practices that may be illegal in your state. There is a federal law that may apply to you if you could be considered a debt collector under the federal Fair Debt Collection Practices Act. In all likelihood, you will not be subject to that law but you will still need to comply with the laws of your state. While each state's laws will differ, you should generally stay away from the following tactics:  Calling at unreasonable hours; Adding additional fees; Purposely delaying collection in order to add more fees; Telling the debtor's employer about the debt; Lying about the debt owed; Making false threats to the debtor.

Summary:
Determine at what point you don't believe you will receive payment without asking. Inquire politely about the money. Decide if you will accept alternate forms of payment. Be more forceful in your payment requests. Continue escalating the rigor of your collection activities. Hire a collection agency. Know what you cannot do.