The document discusses the key aspects of interim payment certificates (IPCs) that contractors should focus on when billing clients. There are two main things to consider: 1) maintaining a good professional relationship with the client through clear communication, understanding their needs, providing expertise, and transparency, and 2) including all necessary details in the bill, such as a covering letter, summary of work completed, requests for inspections, detailed measurement sheets, and documentation of quality control procedures. Providing both relationship-focused client service and comprehensive billing documentation will help contractors successfully achieve certification of IPC bills from clients.