Selected answers from the Dumb SEO Questions G+ community.
Andy Iqseo: Take a look at your site on a mobile. Is it as good as it can be? Are pages so long that it ruins the user experience? Are there big blocks of text? How is the speed of the site?
Lots to think about beside being responsive, although that’s the main one.
Dave Elliott: Make sure everything on your desktop site that is used for ranking(content and schema and links) is on your mobile site and that your sort your page speed and you should be fine.
Steve Wiideman: There`s a big difference in being mobile-friendly and being optimized for mobile.
Most importantly is PageSpeed, cross device compatibility, and a made for mobile experience.
Also, the fewer times a user has to touch their keyboard, the more optimized you become, in working towards a keyboardless world. Think Voice Search, VR, AR and IoT.
He who serves the mobile user best, in SERP presentation, usability, helpfulness, and transaction simplicity will see the most success from the mobile first rollouts.
Michael Martinez: Responsive Websites are not supposed to experience any changes in search performance due to changes in how Google crawls them. About the only way your SERPs could be affected is that your competitors are publishing less content (or fewer navigation links) on their mobile pages.
Casey Markee: Per Google, if you are already mobile responsive you have nothing to worry about. https://www.seroundtable.com/google-responsive-sites-mobile-first-index-24504.html
Michael Stricker: PageSpeed (PageLoad, specifically) has been declared a (minor) rank factor... and the caution is that you don’t want to be among the “slowest in your industry.” Matters greatly on Mobile devices via 3G network connections. So, test. Optimize. Repeat.