Two different starting points
ITIL offers guidance for managing services. ISO/IEC 20000-1 sets requirements for a Service Management System. Treat them as complementary inputs when designing how your organisation manages and improves its services.
Begin with the service scope
Identify the services, organisational boundaries and responsibilities involved. Then tailor practices and controls to your services, business objectives and applicable requirements. Copying a framework diagram into a process document does not establish an effective management system.
Connect activities to evidence
For each control, determine who performs it, when it happens and how its effectiveness can be demonstrated. Policies, records, performance measures and management reviews should connect to actual service delivery.
Keep certification claims precise
Certification assesses conformity against requirements within a defined scope. It should not be presented as an unconditional guarantee that every service will always perform well. Keep improvement objectives and operational measures visible alongside compliance work.
Make the system usable
Use the simplest documents, workflows and review mechanisms that support the required control. Review both whether a practice is followed and whether it helps achieve the intended service outcome.
Further reading: ISO/IEC 20000-1 overview · PeopleCert ITIL practices