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.
Numbers and Numbers and Records and Books _ must be trackable Referring to "invoice #9048," rather than "That invoice I sent you last month, I think on a Tuesday," is much easier to track for both you and your client. Assign numbers to your invoices systematically, consistently and chronologically. Some people number their invoices by year (for example, 2009043 would be the 43rd invoice of 2009). You could also specify a code for the project. For example, ABC06 would be the 6th invoice for the ABC project that you're currently working on. Having an invoice and project numbering system keeps everything in line.