How To Add New Data To Emails

I would like to add data to an email that is generated using Workflow but anytime I add the field name the email no longer contains the data it normally displays.  The message contains &DOCUMENT_APPROVAL_LINES.  But when I add a field above it say like an attribute I know contains data, i.e. Project_Task, then it no longer works correctly.  What is the correct way to add fields now to emails?