To develop an internal audit plan that aligns with ISO 9001 standards, focusing 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 corrective actions.

2. **Identify Critical Areas**: Focus on areas with complex processes or high potential for nonconformities. This includes evaluating compliance with documented procedures, assessing the effectiveness of corrective actions, and ensuring control over outsourced products and services.

3. **Develop an Audit Checklist**: Review documented information such as standards, records, and procedures. Determine what evidence you need to see, what questions to ask, and who to speak with. Write down these questions to form your checklist.

4. **Plan the Audit Schedule**: Establish the frequency, methods, responsibilities, and reporting requirements for your audits. Consider the results of previous audits and the importance of processes when planning.

5. **Conduct the Audit**: Follow the planned itinerary, using your checklist to guide the audit process. Ensure the objectivity of the audit and document the results.

6. **Report and Follow-up**: Communicate audit results to relevant management and document them. Follow up on any issues or improvements identified during the audit.

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