Define what “legacy” actually means
Old technology is not automatically a problem. Legacy becomes costly when the system is unsafe to change, difficult to operate, impossible to integrate or no longer fits the business process.
Modernisation should target those concrete constraints rather than chase a newer stack for its own sake.
Map data ownership before interfaces
The hardest part of replacement is often deciding which system owns each piece of business state during the transition.
Clear ownership prevents two systems from silently diverging while users believe both are authoritative.
Look for seams in the workflow
A good migration boundary is a capability that can be separated with a clear contract: a portal, reporting flow, booking journey, document process or integration layer.
Those seams allow new software to create value before the whole legacy estate is gone.
Plan coexistence deliberately
For a period, old and new systems may need to operate together. Synchronisation, permissions, support and rollback need explicit design rather than optimistic assumptions.
Use real operation to guide the next stage
Once the first modernised workflow is live, support data and user behaviour reveal where the next migration will create the most value.
This is one reason staged modernisation can outperform a long rewrite programme with no production feedback.