The main role of the internal auditor is to acquire evidences that organization complies with requirements of the standard. Depending on whether you are part of internal auditors team or single auditor your roles and responsibilities can vary. Here I will explain the audit performed by a single auditor who has the same responsibilities as the lead internal auditor in case of internal auditor team.
Internal auditor must manage the internal audit process which means establishing internal audit plan (when and which processes will be audited) and the scope of the audit (in this case compliance with ISO 9001:2008). Than you should organize the opening meeting where you present to the auditees the schedule and the scope of the internal audit.
When you start auditing process by process, you need to look at the documents and procedures to see whether they are compliant with the standard or not and than to interview the process own ers and employees to determine whether they follow the defined procedures and do they keep records prescribed by procedures.
If you spot some nonconformity, you should present it during closing meeting at the end of the internal audit. The participants of the closing meeting should be process owners and higher management. Besides nonconformities, you can also present some good practices identified in processes and recommendations for improvements.
After closing meeting internal auditor creates internal audit report and delivers it according to procedure for internal audit.