Set up Image Redirects when URLs Change
If you change image URLs, set up redirects to help them get picked up more quickly.
Prevent Test Site Being Indexed with Canonical
John recommends using a canonical to the main site, although he says that it’s possible for both to be indexed.
301 Is Better for 6 Month Temporary Redirects
For 6 month temporary URL migrations, a 301 redirect is better than 302 to speed up the move.
Keep 301 redirects in place as long as possible
Although Google are able to recognise a site move as a permanent move which doesn’t require the redirect, although some links may not remain completely redirected.
Image Re-Crawling Takes Longer After a URL Change
Images are not crawled very frequently, so when you migrate them to new URLs/domains, it will take a lot longer than pages, perhaps months.
Avoid Redirect Chains
If you change domain and URL at the same time, you can have 2 redirects in a chain, although redirecting directly is preferred. Google can follow more than 5 redirects in a chain, but in separate crawling attempts.
Submit Sitemaps with Changed URLs
If you change many URLs, you should submit a sitemap with the old URLs to Google which will help them pick up the redirects to the new URLs. Webmaster tools will report errors with the sitemap, because it only contains redirecting URLs, but this is fine.