Google recently announced changes to their SEO ranking algorithm that significantly improves the experience of using the web on smartphones. The goal of these changes: to improve search results for smartphone-friendly websites and penalize sites that make mobile browsing difficult.

So, how can you make the most of Google’s mobile SEO ranking algorithm and ensure your mobile site isn’t being punished? Follow Google’s recommendations; understand the impact for e-commerce and publishing sites; and be well aware of common pitfalls for mobile SEO.

In this definitive guide to Google’s new mobile SEO rules, I'll highlight the key ways you can optimize your website to take advantage of these recent changes.

Part 1. Google Loves One-URL and Responsive Websites

Last summer, Google announced that it prefers mobile solutions that maintain the same URL across platforms. In other words, Google prefers sites that work across all kinds of devices — desktops, smartphones and tablets — via a single URL.

However, a more recent announcement on June 11 of this year was the first official acknowledgement by Google that one-URL websites are actually favored in mobile search. From Google’s updated best-practices guide:

"Google recommends webmasters follow the industry best practice of using responsive web design, namely serving the same HTML for all devices."

So, why does Google prefer the one-URL solution?

Reason 1: Social Sharing is the New Black

Whether it's email, Facebook, Twitter, LinkedIn, Pinterest, Google+ or other networks, sharing URLs via social media is essential for content distribution in 2013. Social channels drive traffic as followers click through to your website. This improves organic search results and influences your search rankings, especially when links are picked up by blogs and other media.

Reason 2: Redirects are Slow

Performance penalties for redirects can be serious on smartphones. If you see an “m.” or “mobile.” at the beginning of a URL (e.g. http://www.m.example.com), chances are you needed a redirect to get there.

Visitors coming in from organic search typically land on the desktop website and must then be redirected to the mobile or tablet sites. The length of the redirect delay depends on your connectivity.

For a mobile visitor on 3G, a single redirect may cost up to half a second. And according to KISSmetric's model this can cost 3.5% of your conversions. That means if your e-commerce website makes $100,000 a day, a half second delay will cost you one and a quarter million dollars a year. That's an expensive redirect! Meanwhile, desktop visitors also pay a penalty when they click links for smartphone or tablet sites because they’ll need to be redirected to the desktop experience.

There's another hidden but significant cost with redirects: IT overhead. Large websites are challenging enough to develop and maintain. If you need to cross-reference content in two different places (or three if you create a separate tablet website), the management overhead quickly becomes overwhelming.

Part 3. Mobile Proxies are so 2010

Google's announcement is bad news if you're using a mobile proxy to provide your mobile or tablet website. Although Google continues to provide support for the proxy solution, they explicitly mention that incorrectly configured mobile proxies won't rank as high.

The key takeaway: if you’re going to continue using mobile proxies, be sure to meet Google’s specific annotation provisions!

In truth, very few websites correctly implement these annotations. For instance, only 4.5% of the proxy-based retailers in the Internet Retailer Top 500 list has correctly implemented all the required annotations. Most have a partial implementation or no implementation at all. This demonstrates the compliance challenge and is a very good reason to focus your efforts towards a one-URL solution.

Making Mobile Proxies Work through Annotations

Google updated annotation requirements for websites that use separate mobile URLs (including almost all proxy-based mobile websites). They now require two-way (that is, "bi-directional") annotation. For any large website, being fully compliant with these annotations is a significant, yet important, undertaking. Learn more about Google’s annotation recommendations.

If you have a separate mobile URL, 100% compliance with these requirements means modifying the page markup for every page on both your desktop and mobile websites. You could also put entries into your desktop sitemap, but you'll need to add an entry for every page of your site. Additionally, your separate mobile and tablet websites will need to include a canonical link tag indicating the corresponding desktop content page.

Over half of the websites in the Internet Retailer Top 500 fail to set their canonical tag for pages other than the homepage. 95% fail to set the corresponding desktop annotation.

Part 4. Common Mistakes

Google has identified several common mistakes in smartphone websites that will result in lower rankings. In order, they are:

• Unplayable video
• Faulty redirects
• Smartphone-only 404s
• App download interstitials
• Irrelevant cross-linking
• Page speed

I'll skip discussion of unplayable video as this is becoming much less of a problem as most video providers are now providing mobile-friendly tags using HTML5 video. We’ll leave out page speed too, not because it isn't important, but because it's much too broad a topic to cover in this post.

Let's look at the other four mistakes in more detail!

Mistake 1: Faulty Redirects are Still Really Common

Most mobile web users have experienced the frustration of following a link from Google search and being redirected to the homepage of a mobile website that doesn't contain the content of their search result. With 15% of web traffic coming from mobile, it's astonishing to see how prevalent this mistake is in 2013.

If you follow Google's recommended configuration and have a one-URL site, you don't need to worry about this problem. Otherwise, it pays to make sure your redirects are set up correctly.

Mistake 2: Smartphone-Only 404s, (Almost) a Thing of the Past

We don't see this often anymore, but some websites serve 404s to mobile phones when a mobile-optimized page isn’t available. At the very least, make sure that you serve your desktop content – since smartphones can render it reasonably well. It may not provide the very best mobile experience, but it's much, much better than an error page.

Mistake 3: App Download Interstitials

As a regular mobile web user, I get very frustrated every time I see a full page interstitial asking me to download an app. In the best case the website in question has a mobile-optimized version behind the interstitial. In the worst case, there’s no way to get past the interstitial. Either way, I'll be pressing the back button as quickly as I can to find a more web-friendly alternative, and I'm not the only one.

Google has begun explicitly discouraging this practice by ranking down the search results of sites that present this type of interstitial. Thank you, Google!

Mistake 4: Irrelevant Cross-linking

This practice is better known as incorrect opt-out behavior. If users opt out of your mobile-optimized view, they should be taken to the desktop version of the page, not to your homepage or some other landing page.

Track your opt-outs in analytics. If there are pages where you see mobile visitors regularly opting out, it's a good indication there is something wrong with that mobile page. Common problems include not exposing all of the content of the desktop page or a broken mobile page.

Conclusion

As mobile traffic continues to skyrocket, it’s critical to make the most of Google’s mobile SEO ranking algorithm. By following Google’s recommendations and avoiding common mobile SEO pitfalls, you’ll improve search results for your mobile site.