Across from where you put the recipient's name and contact info, include the details of your invoice. This placement makes it easy to keep track of vital information — for both you and the recipient. You'll want to include: Invoice Number, Date prepared, Payment due date.
Next, you need to specify your payment options — whether you prefer to be paid with cash, a check, a credit card or a service like PayPal. Some companies will offer direct deposit, if you do regular work for them, but more than likely you'll have to send an invoice to request payment every time you complete a project.