Google has begun experimenting with mobile-first indexing, which was first announced in mid-October. The mobile-first index will primarily show mobile results over desktop results, which should be “more useful” to the user base who is searching more and more on mobile.
Google has offered some recommendations for webmasters to prepare for the mobile-first index:
You don’t have to do anything if your site is responsive or dynamic.
If your site is different on mobile and desktop, you should probably make changes.
Have structured markup for both mobile and desktop versions.
Verify your structured markup with the Structured Data Testing Tool.
Avoid large amounts of irrelevant structured markup to your mobile site.
Use robots.txt testing tool to verify your mobile site.
No need to make changes to your canonical links.
Add and verify your mobile site to Search Console if you haven’t already.
Google will continue to index your site if you only have a desktop site.
A functional desktop site is better than a broken, unready mobile site.
Google’s Fast Follow-Up to the Mobile-First Indexing Announcement
Mobile is moving technology forward at an alarmingly fast rate. The mobile-first split that Google said would occur “within months” has begun in the form of this early experiment. However, Google says they will “ramp up this change when we’re confident that we have a great user experience.”
More updates will be on the way once Google refines their processes and systems.