If you have a mobile site, it’s worth remembering that you can actually submits two site maps to Google, one for desktop and one for mobile.

Many webmasters mistakenly believe that you can only submit one sitemap – or in the case of a super-sized one, split it into multiple parts – but you can also submit one just for your mobile URLs, too.

Of course, if your site uses responsive design to serve mobile users, there is no need to create two sitemaps since the URLs are the same for both.  And sitemaps are not a requirement for Google, it just makes it easier for Google to discover all your URLs without having to crawl them first.

Here is Google’s documentation for multiple sitemaps management.

If you are building out your mobile version of your site, especially with separate URLs from your main desktop site, if you don’t quite get your site completely mobile friendly by April 21, you can update your mobile site map as you add each page. Since Google is determining the mobile friendliness ranking signal on a page by page basis, this will allow you to alert Google as soon as you have that new page ready to go so that you can benefit from the ranking signal.

In a English/Hindi Google Webmaster Office Hours, Google also reminds people that you should ensure you have both the mobile site and the desktop site verified in Google Webmaster Tools, such as if you use www.example.com for desktop but m.example.com for mobile.  You need to do this if you want to include both mobile and desktop in the same sitemap, and not do separate ones.  But they say it is often easier to manage it when mobile URLs are on a separate sitemap.

And for a sitemaps refresher, here are the sitemaps best practices.