To develop an internal audit plan that aligns with ISO 9001 standards and focuses on the most critical areas for compliance, you can follow these steps:

1. **Determine Audit Objectives**: Based on ISO 9000:2015 and ISO 19011:2018, your objectives should include verifying the effective implementation and maintenance of the quality management system, compliance with ISO 9001:2015 and internal policies, and suitability for achieving the organization's goals.

2. **Identify Critical Areas**: Focus on areas with complex processes or high potential for nonconformities. This includes evaluating compliance with documented procedures, effectiveness of corrective actions, and management of external providers.

3. **Plan the Audit Schedule**: Establish a schedule that considers the frequency, methods, responsibilities, and reporting requirements of internal audits. Ensure the schedule reflects the importance of processes and results of previous audits.

4. **Develop the Audit Checklist**: Review documented information such as standards, records, and procedures. Prepare questions and identify evidence needed to assess compliance and effectiveness.

5. **Conduct the Audit**: Follow the planned itinerary, ensuring objectivity and thoroughness. Communicate audit results to relevant management and document findings.

6. **Follow-up on Issues**: Address any nonconformities or areas for improvement identified during the audit. Implement corrective actions and monitor their effectiveness.

By focusing on these steps, you can ensure your internal audit plan is comprehensive and aligned with ISO 9001 standards.