Projects are complicated. Lots of agreements and changes are constantly made, these should be managed properly.
Document all changes, variations and agreements on your projects. You should put everything in writing.
The title says it all. Document all communication with your client (and with suppliers and contractors). Even with friendly or familiar clients. Client’s project manager may change, so verbal agreements …
It is important in a project to keep very good documentation. It should be complete, organised, and easy to search (not unorganised folders on lots of team members desks where …