Google Plus gets it's description from the meta item named description. Mine was set to a static string describing the blog, not the content of the entry. I've fixed it. Here's how I did it.
Recently I've ben playing with Google Plus (G+) a lot. I noticed when I shared items from my blog, however, that the decscription that G+ grabbed automatically wasn't very good. Turns out it's getting the description from the meta item named description in the header. My blog was setting that to a static string.
I don't know if I just have a bad set of templates (could be--they're old and I've hacked them a lot), but mine didn't put anything about the blog entry in the detail page's description. I use MovableType, so I put the following in the HTML header in the Individual Archive template:
<meta name="description" content="<$mt:EntryExcerpt$>" />
MovableType's EntryExcerpt tag is smart in that if you've filled in the "Excerpt" box when you create the entry, it will use that. If the "Excerpt" box is empty, MT generates one from the first N words of the blog entry body. I usually just leave it empty, but I'll start using it now if the first paragraph isn't as descriptive as I'd like.
So, now my blog entries are more sharable on G+. Who know's, it will probably help them be more findable in search results too.