Before you change anything
- List every page address. Use your sitemap and Search Console, and include pages that aren't in your menu.
- Note your best pages. Search Console shows which ones bring in visits. Keep their content.
- Keep the same addresses if you can. If only the design or hosting changes, this is the safest route.
- Check what else uses your domain. Email depends on your domain settings, so don't lose them.
If the addresses change
- Redirect each old address to its matching new page. Google recommends permanent redirects, such as 301, and says they don't lose ranking value.
- Avoid long chains. Google's advice is ideally no more than 3 redirects in a row.
- Check the page settings. Make sure the new pages aren't marked to stay out of Google, and that their canonical tags are right.
- Test the redirects before and after launch.
- Send the new sitemap in Search Console. If the domain itself changes, also use its Change of Address tool.
- Keep the redirects. Google says generally at least 1 year. We'd keep them for as long as you can.
If only the hosting changes
Copy the site to the new hosting and test it, then update your domain settings. Lowering the DNS TTL a week before helps the change happen quickly. Keep the old hosting running until no visitors reach it. Google may crawl less for a short time, then pick up again over the next few days.
Mistakes that cause most of the damage
- Pointing every old address at the home page, instead of the matching page.
- Deleting pages that were bringing in visits, because they looked old.
- Leaving the test site's block on Google in place after launch.
- Losing email during the switch.
What to expect afterwards
Your position may go up and down for a while. Google says that's normal and that it settles over time, and that a small to medium site can take a few weeks for most pages to move. Check Search Console each week for pages that drop out or show errors, and fix them quickly.
Sources: Google, site moves with URL changes, Google, redirects, Google, changing hosting.