1. Take stock
List all pages of the old website and see which ones bring visitors and which ones generate inquiries. The data comes from Search Console, Analytics and a crawl of the site. Often it turns out that an old blog post from 2019 brings in more visitors than the home page.
2. Define structure and content
Then you decide: which pages stay, which get merged, which get dropped? Pay attention to what people were searching for when they landed on a page. You don't delete a page that is found easily just because it doesn't fit into the menu in the new design.
3. Redirect plan
Every important old address gets a permanent redirect (301) to the matching new page. So /leistungen/badsanierung.html to /badsanierung, not simply everything to the home page. Many people do that, and Google usually treats it like a deleted page.
4. Technical check before going live
Before the new site goes live, check the following on the test environment:
- Titles, descriptions and headings of every page
- Internal links and navigation
- Canonical tags and indexing (the classic mistake: "noindex" from the test phase stays in)
- Sitemap and robots.txt
- Loading time and display on mobile
5. Launch and monitoring
On the day of the switch, you submit the new sitemap in Search Console. In the weeks that follow, regularly check 404 errors, indexing and traffic. If an old address turns up without a redirect, add one right away. The faster, the less Google notices.