Agree what completion means
Different stakeholders may have different expectations of completion. A project plan should make those expectations visible through a defined scope, deliverables and acceptance criteria.
Build evidence as work progresses
Design decisions, configuration records, test results, dependencies and open items are easier to maintain throughout implementation than to reconstruct at the end. The handover pack should be an evolving part of delivery.
Plan the move into operations
Confirm who accepts the system, who supports it, what remains open and how changes will be controlled. The support model and service levels belong in the agreed engagement, alongside the technical solution.
This is a general perspective on engagement design. Specific recommendations depend on the agreed scope and operating environment.