After taking and passing ITIL 4 Foundation, you may take any of the 5 courses in the ITIL 4 Framework Certification Structure, in any order:
To obtain the ITIL Managing Professional (MP) designation, you will need to take and pass all the 4 courses under it while for the ITIL Strategic Leader (SL) designation, both courses under it.
If you are working in IT in a service desk or IT operations, it is highly recommended to start with ITIL Specialist: Create, Deliver & Support. Around 70% of what people do inside ITIL is covered in this course such as how to create a service, how to deliver and operate that service, and how to support your users.
Managers and executives should start with ITIL Strategist: Direct, Plan & Improve which is a course available for both the Managing Professional and Strategic Leader designations. This course focuses on measures, metrics, KPIs, and how to plan from a vision down through your strategy, into your plans, and how you are going to execute that vision.
ITIL Specialist: Drive Stakeholder Value is much more focused on the business environment, selling, marketing, and the customer journey. This is best suited for those who work outside of the IT environment.
Agile ways of working and software development are given focus in ITIL Specialist: High Velocity IT. This course talks about how IT can keep up with the changes in today's environment.
So the next course to take would really depend on which would best be suited for your day-to-day activities in the workplace.