If you are using Responsive Web Design, use meta name="viewport" tag to tell the browser how to adjust the content. If you use Dynamic Serving, use the Vary HTTP header to signal your changes depending on the user-agent. If you are using separate URLs, signal the relationship between two URLs by tag with rel="canonical" and rel="alternate" elements.
Can you offer any commentary that is more specific to web-based stores? I definitely see the value in some of this and have made a few positive changes to my site, but I’m not a blogger and am ideally looking to direct more traffic to the site through other means. As it stands, we get only a few orders/month, and I’d like to dive deeper into how we can simply (though not necessarily easily) expand our market.
When would this be useful? If your site has a blog with public commenting turned on, links within those comments could pass your reputation to pages that you may not be comfortable vouching for. Blog comment areas on pages are highly susceptible to comment spam. Nofollowing these user-added links ensures that you're not giving your page's hard-earned reputation to a spammy site.
Paid search results are those in the top and bottom of the results page, indicated by the small “ad” icon. These are placements that businesses pay for to show up when users search specific keywords. Google Ads can be a very effective way of utilizing ad spend for those who are new or struggling to compete against businesses that rank higher in organic search results. It’s also great for businesses targeting keywords with high revenue potential.