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 the effectiveness of processes in achieving intended results.

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. Use the checklist to guide the audit and gather evidence.

6. **Report and Follow-up**: Communicate audit results to relevant management, document findings, and follow up on any issues or improvements identified.

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