Critical areas to prioritize focus during implementation

This answer will depend on the results of risk assessment and the identification of legal requirements (e.g., laws, regulations, and contracts), because they will allow you to identify the areas which concentrates the most relevant risks, and which are subjected to the greatest impacts in case of legal requirements noncompliance.

Besides the areas where ISO 27001 will be implemented, you also should add some emphasis on management support, project management, and training, to ensure availability of resources and employee engagement.

For further information, see:
- ISO 27001/ISO 27005 risk assessment & treatment – 6 basic steps https://advisera.com/27001academy/knowledgebase/iso-27001-risk-assessment-treatment-6-basic-steps/
- The basics of risk assessment and treatment according to ISO 27001 [free webinar on demand] https://advisera.com/27001academy/webinar/basics-risk-assessment-treatment-according-iso-27001-free-webinar-demand/
- How to identify ISMS requirements of interested parties in ISO 27001 https://advisera.com/27001academy/blog/2017/02/06/how-to-identify-isms-requirements-of-interested-parties-in-iso-27001/
- ISO 27001 project – How to make it work https://advisera.com/27001academy/blog/2013/04/22/iso-27001-project-how-to-make-it-work/