You might even come with a written list of agenda items. Choose your seating carefully. Don't let an agency official hide behind a desk or sit at the head of a table. This gives control over the meeting. Refer to them as they refer to you.
Titles carry authority.
Bring your documents, such as letters, to the session. Chair the meeting. Review the circumstances or case leading to the meeting, the law, and other facts. Present your demands or positions clearly. Outnumber your opponents.