Why visits get lost
When a site is rebuilt, page addresses often change, content gets removed and titles change. For search engines it's as if the old site vanished and a new one arrived, to be learned from scratch. If old links meanwhile lead to pages that no longer exist, visits drop.
Start with an analysis
Before deciding what to change, look at what works: which pages get visits, which searches they come from, which are linked from other sites. This data lives in your analytics and in Google Search Console, if they're active.
The address map
For each page of the old site you decide: it keeps its address, merges with another, gets rewritten or is removed. Every old address needs a destination on the new site, even if the page no longer exists: usually the closest page by content.
- Pages that stay: same address where possible
- Merged pages: redirect to the new one
- Removed pages: redirect to the closest
- Never leave old addresses without a destination
Redirects and checks
Permanent redirects (status code 301) tell search engines and browsers that a page has moved. They must be set up before publishing and tested one by one.
After the switch, for a few weeks, check errors, pages not found and visit trends. Some fluctuation is normal; a sharp drop points to a problem to fix straight away.