Mobile-first Indexing: What is it? How it Works? and What to do next?

Earlier this week, Google began sending mobile-first indexing notices to webmasters of the websites who are using search console. Previously, mostly the sites that were not mobile-friendly were first moved but now, even mobile-friendly sites are being moved. So, now that Google has officially rolled out mobile-first indexing, I am going to explain what is mobile-first indexing, how it works and what should be the next steps to be followed as the best practices.

What is mobile-first indexing?

 Before I try to explain about mobile-first indexing, let us look at the description provided by Google when the same was announced:
 “To recap, our crawling, indexing, and ranking systems have typically used the desktop version of a page's content, which may cause issues for mobile searchers when that version is vastly different from the mobile version. Mobile-first indexing means that we'll use the mobile version of the page for indexing and ranking, to better help our – primarily mobile – users find what they're looking for
 This was much needed as per the fact that majority of Google searches are made on mobile but the ranking results are still based on a system that ranks pages on the desktop first.
Q) Wait, aren’t the mobile pages and desktop pages for the sites similar?
A) No, mobile pages often differ from their desktop alternatives and it doesn’t make sense to send people to the pages which are optimised for desktop when they are using mobile to search the same.
 So, this shifts the priority to the mobile version of the pages in order to create better search results and experiences for which Google is known for.
Yes, this calls for a few questions, some of which I will try to address as we move forward.

How mobile-first indexing works and what will be its effect on SEO and Search rankings?

The following visualisation will help to understand this better:
As the graphic above shows, the default behaviour will be to crawl the mobile version of your page when there is one available otherwise it reverts to indexing your desktop page and the determines its ranking as normal.

How it will affect SEO and search rankings?

It looks like that there will be lot of changes the way Google search operates but the impact on SEOs and website owners will be quite minimal and surely there is no need to panic.
Regarding the effect on Search Ranking: it entirely depends on how your website and pages are optimised for mobile.
#1 If your website is responsive i.e. your mobile and desktop pages are same – then you shouldn’t be affected by mobile-first indexing as this is the design approach which Google recommends for mobile optimisation.
#2 If your website provides separate mobile and desktop pages to users then in this scenario the mobile version will be crawled first and based on this your search rankings could be impacted, if and only your mobile pages lacks structured data and metadata, the mobile pages are poorly optimised for mobile or they aren’t correctly verified in Search Console.
So, If you follow the usual best practices for mobile optimisation then more or less it should be fine. You can find out best practices for mobile-first indexing at Google Developers for which the quick summary is:
Desktop only
No change. The mobile version is the same as the desktop version.
Your site is desktop only and doesn't have a mobile-friendly version.
Responsive web design
No change. The mobile version is the same as the desktop version.
Your site adjusts for screen size.
Canonical AMP
No change. The mobile version is the same as the desktop version.
All your web pages are created in AMP HTML.
Separate URLs
Google prefers the mobile URL for indexing. To prepare for mobile-first indexing, follow our best practices.
Each desktop URL has an equivalent different URL that serves mobile-optimised content. This site type is also known as an m-dot site.
Dynamic serving
Google prefers the mobile optimised content for indexing. To prepare for mobile-first indexing, follow our best practices.
Your site serves different content based on the user's device. Users only see one URL.
AMP and non-AMP
Google prefers the mobile version of the non-AMP URL for indexing. If your non-AMP mobile version uses dynamic serving or separate URLs, follow our best practices.
Your site has both AMP and non-AMP versions of a page. Users see two different URLs.
How will you come to know that your site is migrated to mobile-first indexing?
Most of the people who have their site submitted to Search Console have received an email notifying that your mobile site has been migrated over to mobile-first indexing and it looks like the graphic below:
After this email, you will see a significant increase in the crawl rate from Google’s mobile bot and the mobile pages will appear in the search results if there are separate mobile pages; for responsive websites nothing should majorly change. But it is always good to run an audit post getting the notification and perform the required changes in accordance with mobile-first indexing best practices.
What should be done once my site is migrated to mobile–first indexing?
This question is relevant if you have separate mobile and desktop pages or you use dynamic content delivery for different devices, if any of this is yes then its suggested to perform the following steps:
-      Your servers are tuned properly so that they can handle increase in crawl rate for the mobile version of your website.
-      Use canonical tags properly between mobile and desktop versions
-      Mobile & Desktop pages should have the same content
-      Both version have the required structured data & metadata and are submitted properly in Search Console.
-      Robots.txt should be optimised for both mobile and desktop versions.
Majorly all the above points are part of usual optimisation best practices and if these are followed then you should not worry about the change. Just get a basic audit done and fill up the loop holes if there are any and if need any help can contact me via email.