Google's search indexing is kind of a big deal - having a high spot in relevant searches for the world's biggest search engine can literally make or break a business. So if you don't want your site to lose its spot, you'd better make sure your website looks good when accessed from a mobile browser. Starting on April 21st, Google's search algorithm will incorporate whether or not a site is "mobile-friendly" when ranking its appearance in search results. Google announced the change on its Webmaster Central blog:

Starting April 21, we will be expanding our use of mobile-friendliness as a ranking signal. This change will affect mobile searches in all languages worldwide and will have a significant impact in our search results. Consequently, users will find it easier to get relevant, high quality search results that are optimized for their devices.

So if you want to keep your good search ranking, or alternately improve your ranking even more, you can use Google's guidelines, a mobile-friendly test, and this mobile usability report to test your compliance with what Google thinks is a good showing on mobile browsers. Whether a site is adaptive to a range of screen sizes or resolutions (like the new version of Android Police) or shows completely different formatting for phones and tablets (like the old version of Android Police), you should be covered.

Google also announced changes to Search that will show more relevant apps from the Google Play Store when you search while signed in.