The tags you put in the head of your Blogger template to support Twitter Cards and Open Graph.
<!-- Begin Open Graph metadata -->
<meta content='summary' name='twitter:card'/>
<meta content='@<your twitter account>' name='twitter:site'/>
<b:if cond='data:blog.metaDescription'>
<meta expr:content='data:blog.metaDescription' name='og:description'/>
<b:else/>
<!-- Twitter Cards require a description but blogger posts don't always have one -->
<meta content='<Default Post Description>' name='og:description'/>
</b:if>
<b:if cond='data:blog.pageType == "item"'>
<!-- For the individual blog post page -->
<meta content='article' property='og:type'/>
<meta expr:content='data:blog.title' property='og:site_name'/>
<meta expr:content='data:blog.pageName' property='og:title'/>
<b:if cond='data:blog.postImageThumbnailUrl'>
<meta expr:content='data:blog.postImageThumbnailUrl' property='og:image'/>
</b:if>
<b:else/>
<!-- Index, search etc. -->
<meta expr:content='data:blog.title' property='og:title'/>
<meta content='website' property='og:type'/>
<meta content='<Default image url here>' property='og:image'/>
</b:if>
<meta expr:content='"<your locale>"' property='og:locale'/>
<meta expr:content='data:blog.canonicalUrl' property='og:url'/>
<!-- End Open Graph metadata -->