According to the ISACA CGEIT Exam Candidate Guide, one of the tasks under the domain of Strategic Alignment is to "understand the current vision and direction of the enterprise and identify how IT can best support it."1 This task should be done first when developing an IT strategic plan that supports an enterprise's business goals, because it provides the basis for aligning IT with the business strategy and priorities. By understanding the current vision and direction of the enterprise, the IT strategic plan can identify the gaps, opportunities, and challenges that need to be addressed by IT, as well as the expected outcomes and benefits that IT can deliver to the enterprise23. The other options are not the best actions to perform first in this scenario. Ensuring that IT drives business goals, analyzing benchmarking data, and performing a business impact analysis (BIA) are all useful steps or methods for developing an IT strategic plan, but they are not the starting point. They should be done after understanding the current vision and direction of the enterprise, based on the alignment and integration of IT with the business strategy and goals23. References:
1: https://www.isaca.org/-/media/info/cgeit/cgeit-exam-candidate-guide.pdf
2: https://www.cascade.app/blog/it-strategic-plan
3: https://www.projectmanager.com/blog/it-governance-frameworks-definitions