The optimal way to implement an ISMS according to ISO 27001 is to follow this sequence:
1. Obtain management support
2. Set up project management
3. Set up document management
4. Analyze internal context
5. Identify security requirements of interested parties
6. Define the ISMS scope
7. Write a top-level Information Security Policy
8. Define the risk assessment and treatment methodology
9. Perform risk assessment and risk treatment
10. Write the Statement of Applicability
11. Write the Risk Treatment Plan
12. Define how to measure the effectiveness of ISMS
13. Implement security controls
14. Implement training and awareness programs
15. Operate the ISMS
16. Monitor and measure the ISMS
17. Carry out an internal audit
18. Perform the management review
19. Execute corrective actions

To see the certification steps, you can ask a question like "How to prepare for a certification audit?"