Discover what the application really does
Business rules often live across database packages, triggers, form logic, and operational habits. Inventory these dependencies with the people who use and maintain the application. Map critical workflows before selecting a migration approach.
Separate logic from presentation
Review which database-side rules can remain and which form-specific behaviors need redesign. APEX provides a browser-based application model, so some interactions need to be rethought rather than mechanically reproduced.
Deliver a useful vertical slice
Choose a bounded workflow, build its end-to-end replacement, and validate it with users. Include security, integrations, desktop and mobile behavior, and reporting. A small complete release exposes risks earlier than a large untested conversion.
Plan the transition
Define acceptance criteria, regression testing, data reconciliation, cutover, rollback, and user training. Cloud readiness and maintenance improvements should be explicit design goals, assessed against the actual environment.