The best time to bill customers is as soon as it's practically possible. Service providers can bill clients the day the service is completed-or sooner if you incur substantial expenses along the way. If you send products to customers, include the invoice with the shipment.
Make sure your invoice is professionally designed, with the word "invoice" clearly printed across the top. Your company's name, address and phone number should also be prominent.
Send the invoice to the person responsible for remitting payment. Your invoice should describe the product or service provided, specify the exact charges, state the total amount due and identify the person who placed the order.
To speed payment, state "payment due upon receipt" on your form. A really smart way to speed the process is to offer a discount if the bill is paid within 10 days.
Excerpted from Get Smart: 365 Tips To Boost Your Entrepreneurial IQ