Adding an XML sitemap to your site is not only a good way to ensure all of your pages are properly indexed, but it’s also the way Google would like you to tell them where your content is. That’s right folks, Google is getting you to do their work for them. So why do you need an XML sitemap anyway?
According to Google, these are particularly helpful if:
1) Your site has dynamic content that you would like to be searchable. Dynamic content is hard to get picked up unless it is linked to or Googlebot happens to stumble across it.
2) If you have pages that are not easily discoverable, or you use a lot of AJAX.
3) If your website is very new and does not have a lot of links pointing to it, then Google will take longer to find it and prioritize it.
4) If you have a large section of content that is archived, or not well linked.
So basically, if you have crappy site architecture, then you’ll want to have an XML sitemap. You can create one here for free, or if you are in WordPress, download the Google XML Sitemaps plugin. Once you have your sitemap, and you’ve placed it in the root folder of your website (some of you may have to FTP the file up to the server), then all you have to do next is go into Google Webmaster Tools, create your account, add the little meta tag to verify ownership, and then add the sitemap. It’s actually pretty easy to do, and should take you about 15 minutes from creating the sitemap, placing it, and then adding it to WMT.
Video XML Sitemaps
Another way to let Google know what kind of content you have is to submit a video XML sitemap. You would put it in the same place in WMT, or you can add a URL path to the sitemap in your robots.txt file. Check out these guidelines for video XML sitemaps.