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, evaluating compliance with documented procedures and legal requirements, and assessing the effectiveness of corrective actions.

2. **Identify Critical Areas**: Focus on areas with the highest potential for nonconformities or those that are most complex. This includes processes related to quality control, nonconforming product management, process monitoring, and evaluation.

3. **Develop Audit Criteria and Scope**: Define the criteria and scope for each audit. This involves determining which ISO clauses are relevant, such as those related to quality control activities, nonconforming product management, and process monitoring.

4. **Plan the Audit Schedule**: Create a schedule that outlines when each audit will take place, considering the importance of processes and results of previous audits.

5. **Prepare the Audit Checklist**: Review documented information, such as standards, records, and procedures. Write questions that will help you gather evidence on whether the requirements of the standard are met.

6. **Ensure Auditor Competence**: Make sure your internal auditors are competent and objective. They should not audit their own work and should have the necessary training on audits and ISO 9001:2015.

7. **Conduct the Audit**: Follow the planned schedule and checklist to conduct the audit, ensuring all requirements of the standard are covered.

8. **Report and Follow-up**: Document the audit results and communicate them to relevant management. Follow up on any issues or improvements found during the audit.

By focusing on these steps, you can ensure your internal audit plan aligns with ISO 9001 standards and addresses the most critical areas for compliance.