Here’s how:
1. Sign in to your Google Webmaster account.
2. Add your Tumblr blog URL to your website lists.
3. Verify your Tumblr blog.
Copy the Metatag from your Google Webmaster. Now sign in to your Tumblr account. At Dashboard, find ‘Customize’ in the right sidebar, click it. Find Theme, second at top left and click on it. Click on Custom HTML at the bottom, then find and paste the metatag given by Google just after that line. Save and close. Now go back to your Google Webmaster click on Verify.
4. Submit Sitemap.
As Tumblr is not what we call self hosted website, we can’t create and submit sitemap.xml file to Google. But there’s a 3rd party solution for that, in tumblrMap. Submit your Tumblr login, then follow the steps. You’ll need to add another metatag given by tumblrMap, you can follow instructions on step 3 above. You can see reports on your tumblrMap account, associated with your Tumblr blog (s) Sitemap.
5. Backup your Custom Theme.
As easy as 1 click from the theme dashboard, you can change your Tumblr theme. But that also means you’ll miss the metatags you inserted, as well as manual Disqus comments or any other third party codes you had on you old theme. Backing up will make your life easier anytime you want to switch themes/
