On your public-facing website use the XML Sitemap and Robots.txt file to optimize your website for Internet search engines.
When building public-facing websites with SharePoint 2013 you should disallow anonymous users from overriding the Master Page on your website.
Using Device Channels in SharePoint 2013 you can separate your authoring and publishing experience. This will allow you to optimize your public-facing website for visitors and search engines without losing any of the standard content management capabilities of SharePoint 2013.
On your public-facing website consider enabling the anonymous search REST API to publish your content to other channels such as topic sites and mobile apps.
When using Device Channels on your website set the Vary: User-Agent response header to let Internet search engines know that different HTML is rendered to different browsers.