[header] How to prepare a customer invoice [title] Write or type your company's contact information on a sheet of paper, spreadsheet or other electronic record keeping system. [step] Remember to include an email address and phone number where they can contact you with questions. [title] Create an original customer invoice number using letters, numbers or both. 
[step] A customer invoice number can be as simple " job-001 " or more complex, such as " smith-job-001. " the second example is useful for repeat customers because it includes their last name along with a job number.