Your opening meeting, if there is one, will depend upon the audit specifics. If you re doing an internal audit of a manufacturing area, you might hold the meeting right there - standing - at or in the area. Or - you might want to grab a conference room and more thoroughly go over the agenda and other issues.
The level of formality will depend upon you and your company. And the specifics. If you are doing a third party audit the meeting is typically quite formal. Formal audits almost always have agendas. In the case of an audit by a registrar you will find they have very formal, detailed agendas.
The opening meeting:
Introduces the audit team to the department members
Reviews the audit plan, scope and objectives for the audit
Establishes the official communication link between department representative and audit team
Review findings from document review
ISO 19011 - Quality and Environmental Management Systems Auditing Forum Discussions