How do I migrate my website without losing SEO?

The single most important step is redirects. List your existing URLs, decide where each one lives on the new site, and set up permanent 301 redirects from old to new. That tells Google the page has moved and passes most of its ranking value across. Skipping this is the usual reason sites lose traffic after a relaunch.

Keep as much continuity as you can. Retain the same URLs where possible, preserve page titles, meta descriptions, headings, and the content that already ranks, and don't accidentally block the new site from being indexed — a stray "noindex" or robots disallow left over from staging is a classic, costly mistake. Update your XML sitemap and internal links to point at the new URLs.

Verify rather than assume. Crawl the old and new sites to catch broken links and missing redirects, submit the new sitemap in Google Search Console, and watch coverage, rankings, and traffic for a few weeks afterwards. A small, temporary dip while Google re-crawls is normal; a sustained drop usually points to a redirect or indexing problem you can still fix.