The BEST way for an organization to ensure that incident response teams are properly prepared is by conducting tabletop exercises appropriate for the organization.
Tabletop exercises are an effective way to test and validate an organization's incident response plan (IRP) and the readiness of the incident response team. These exercises simulate different scenarios in a controlled environment and allow the team to practice their response procedures, identify gaps, and make improvements to the plan. By conducting regular tabletop exercises, the incident response team can stay current with changes in the threat landscape and ensure that they are prepared to respond to incidents effectively.
According to the Certified Information Security Manager (CISM) Study Manual, "Tabletop exercises are a valuable tool for testing and validating the effectiveness of the IRP and the readiness of the incident response team. These exercises simulate different scenarios in a controlled environment and allow the team to practice their response procedures, identify gaps, and make improvements to the plan." While providing training from third-party forensics firms, obtaining industry certifications, and documenting multiple scenarios for the organization and response steps can all be useful in preparing incident response teams, they are not as effective as conducting tabletop exercises appropriate for the organization.
Reference:
Certified Information Security Manager (CISM) Study Manual, 15th Edition, Page 324.

Information security governance is MOST important to have in place to help ensure an organization's cybersecurity program meets the needs of the business. This is because information security governance provides the strategic direction, oversight and accountability for the cybersecurity program. It also ensures that the program aligns with the business objectives, risk appetite and compliance requirements of the organization. Information security governance involves defining roles and responsibilities, establishing policies and standards, setting goals and metrics, allocating resources and monitoring performance of the cybersecurity program.

Consistent security is the primary reason for integrating the various assurance functions of an organization for the information security manager because it ensures that the security policies and standards are applied uniformly and effectively across different domains, processes, and systems of the organization. Comprehensive audits are not the primary reason for integrating the various assurance functions, but rather a possible outcome or benefit of doing so. A security-aware culture is not the primary reason for integrating the various assurance functions, but rather a desirable state or goal of the organization. Compliance with policy is not the primary reason for integrating the various assurance functions, but rather a basic requirement or expectation of the organization. Reference: https://www.isaca.org/resources/isaca-journal/issues/2016/volume-4/integrating-assurance-functions https://www.isaca.org/resources/isaca-journal/issues/2017/volume-3/how-to-measure-the-effectiveness-of-your-information-security-management-system