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 the most complex processes and those with a high probability of nonconformities. This includes areas like quality control activities, nonconforming product management, process monitoring, and top management's leadership and commitment.

3. **Develop Audit Criteria and Scope**: Define the criteria and scope for each audit. This involves reviewing documented information such as standards, records, procedures, and work instructions.

4. **Prepare an Audit Checklist**: Create a checklist based on the standards and internal procedures. Include questions that provide evidence of compliance and effectiveness, such as whether quality control activities are performed according to plan and if corrective actions are developed for nonconformities.

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

6. **Conduct the Audit**: Follow the planned itinerary and sequence, ensuring objectivity and competence of the auditors. Collect evidence through interviews, document reviews, and observations.

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

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