The short answer
Inventory valuable URLs, map each one to the closest useful destination, validate the new site before release, implement direct permanent redirects and monitor both properties while search engines process the move.
Build the source inventory
Combine crawls, sitemaps, analytics, Search Console, backlink evidence and business-critical routes. Mark which URLs retain, merge, redirect or retire and who approves the decision.
Design the destination map
Redirect each valuable URL to the closest relevant destination. Avoid sending unrelated pages to the homepage, and resolve chains before launch.
- Old URL and final destination
- Reason and content owner
- Status code and redirect source
- Pre-launch and post-launch acceptance check
Test the new site in a controlled environment
Check rendered content, canonicals, robots rules, sitemaps, internal links, structured data, forms, analytics, performance and error behaviour before the production switch.
Release one controlled change
Where practical, avoid combining a domain move, CMS replacement, redesign and content rewrite into one untraceable event. Keep rollback ownership and monitoring ready.
Monitor until the move settles
Crawl both sites, test redirect samples, submit the new sitemap, watch indexation and query landing pages, and keep permanent redirects for at least the period advised by current Google guidance.
Primary sources used
External guidance is linked so you can check the current source and context directly.