The best practices for conducting internal audits under ISO 9001:2015 include:

1. **Planning the Audit Schedule**: Develop a schedule that covers all areas of the Quality Management System (QMS) and ensures compliance with ISO 9001:2015 requirements.

2. **Planning the Process Audit**: Prepare by reviewing the standard, internal documentation, and creating a checklist of topics to cover during the audit.

3. **Conducting the Audit**: Ensure auditors are competent and impartial, and gather evidence through interviews, document reviews, and observations to determine if the QMS is effectively implemented and maintained.

4. **Reporting on the Audit**: Report findings to relevant managers, highlighting both minor and major nonconformities.

5. **Follow-up on Issues or Improvements Found**: Address nonconformities by controlling and correcting them, evaluating the need to eliminate their causes, implementing corrective actions, reviewing the effectiveness of these actions, and updating documentation if necessary.

Non-conformities should be addressed by:

1. **Controlling and Correcting the Nonconformity**: Take immediate action to control and correct the issue and deal with any consequences.

2. **Evaluating the Need to Eliminate Causes**: Determine if actions are needed to prevent recurrence by identifying and eliminating root causes.

3. **Implementing Corrective Actions**: Take steps to correct the root causes and prevent future occurrences.

4. **Reviewing Effectiveness**: Check if corrective actions have been effective in resolving the issue.

5. **Updating Documentation**: Make necessary changes to documentation to reflect new procedures or responsibilities.