Work on the assumption that anything you put in the project file may some day be looked at in a court of law.
Be careful with every document, photo, memo, drawing, email that is put in the project folder. Make sure it is something that you would be happy for anyone to see.
Don’t put project instructions in the same email as a personal note.
If you want to congratulate a client on a personal topic for example the birth of a child), do not also include project information, questions or instructions in that same email. Send a completely separate email, even if it just a moment later. It is important to separate these, as project related correspondence may and probably should by filed in the project file.