With more internet users browsing the web using their Mobile devices, webmasters and web owners should anticipate these people with careful planning.

Google's crawling, indexing, and ranking systems typically look at the desktop version of a page's content. But this may cause some issues for mobile searchers when that version is vastly different from the mobile version.

With mobile-first indexing that was introduced in 2016, Google uses the mobile version of the content for indexing and ranking, to help meeting the increasing demand of mobile users.

As it previously said, websites that use responsive web design properly and also use the appropriate dynamic content serving, generally don't have to do anything. But still, Google is providing more advice around getting ready for the mobile-first index.

• Make sure that the mobile version of your site also has the important, high-quality content. This includes text, images (with alt-attributes) and videos, all in the usual crawlable and indexable formats.
• Structured data should be available on both mobile and desktop version of your website. Ensure URLs within the structured data are also updated to the mobile version on the mobile pages.
• Metadata should also be present on both versions of your website. This provides hints about the content on a page for indexing and serving.
• No changes are necessary for interlinking with separate mobile URLs (m.-dot sites). If your website uses separate mobile URLs, you just need to keep the rel=canonical and rel=alternate link elements between the two versions.
• You need to check on the hreflang links on separate mobile URLs. When using link rel=hreflang for internationalization, you need to link between mobile and desktop URLs separately. Your mobile URLs' hreflang should point to the other language/region versions on other mobile URLs, and similarly link desktop with other desktop URLs using hreflang link elements there.
• Make sure that your server(s) that host your website have enough resources to handle the potentially increased crawl rate. This however, won't affect those websites that use responsive web design and dynamic serving, as it only affect websites where the mobile version is on a separate host (m.-dot sites).

Google will evaluate websites it crawled and indexed independently, based "on their readiness for mobile-first indexing based". When they meet the above criteria, Google will transition them when ready.

Webmasters and web owners should know when their website is friendly for mobile users when they see an increased crawling rate by the 'Smartphone Googlebot' on their log files and inside the snippets in the results.

And also, the content on the Google cache pages, will be from the mobile version of your web pages.

According to the company, it is cautious about those websites that want to be included.