Their Details and Yours _ must be complete This is basic stuff, but you can't afford to forget it. In addition to the client's address, make sure to include the name of the client's contact person who handles your account! A company with three employees can figure out what you're doing; but in big companies, invoices get misplaced, especially if there's confusion over who belongs to which project. You'll also need your company name, your name, address, telephone number and email address. If they have any questions about the charges, contacting you should be as easy as possible.
Itemized List of Services _ must be specific People want to know what they've paid for. Most people will not pay for something described merely as "Design." Tell them exactly what they have received: e.g. "Design of three_page static website for Sporting Goods Department." Be as specific as possible. In five years, would both you and the client know what you meant by your description? Also, specify whether the charge is project_based or hourly.