It's 2018 and Google is little by little implementing the mobile first indexation process, crawling the mobile version first making it the primary version of the website, caching it instead of the Desktop one.
Optimised mobile-friendly will be ranking better for both mobile and desktop than a website with a poor mobile version. Having a responsive websites simplifies the problem. Nowadays, it’s essential to have a site that responds to all device sizes.
It still means checking and optimising load time and page speed, images and navigation. (40% of mobile online shoppers abandon the site after 3 seconds).
On the SEO classic side, checks should be done for meta titles and description, canonical and hreflang attributes, links to XML sitemaps, robots instructions and schema markup.
AMP helps to load your web pages much faster than regular HTML so this can help you if your mobile version is not performing well.
Although open-source, it is “lead” by Google and Google caches the content on their own cache to speed up load time.
AMP improve server performance and UX, however, it has some drawbacks to consider such as less programming capabilities, time and resources necessary to make the change, and some analytics data you could not access due to the pages being cached at Google.
If you offer a native app you might consider using this web applications that can appear to the user as traditional applications.
They offer quick loading and can be used offline but most importantly as search engine friendly. with its JSON-LD formatted API.
The current cons are that not all browsers are supported especially Safari which covers nearly half of the mobile browser market. Same with the device software with no support functionality on iOS devices.
PWAs can be combined with AMP (PWAMP) which create super fast web apps with offline access and search engine friendliness.
More and more Local and Google-cached, the importance of Google MyBusiness. Mobile-First Really Means Cloud First
Key for customising your local presence on Google Maps which shows in SERPs and collecting star ratings and reviews. Since the content that you submit to Google My Business is already hosted in a database in Google’s cloud, they don’t need an API. Google is pushing this.
As Sundar Pichai, Google's CEO declared “We will move from mobile first to an AI first world."
Part 2 of this series will go deeper in looking at other Google's technology which is leading in this direction such as Firebase, Action schema and Dynamic Linking.