Now that we’ve got proper titles, we should start to focus on meta descriptions. The meta description can be used by search engines to show in the snippet, it’s the black piece of text shown beneath the URL. The meta description is usually only used when it contains the keyword the searcher was searching for.
Some plugins, most specifically the All in One SEO plugin, use so called “automated descriptions”. They use the first sentence of a post to fill the meta description by default. That’s not very smart. That first sentence might be an introductory sentence which has hardly anything to do with the subject.
Thus, the only well written description is a hand written one, and if you’re thinking of auto generating the meta description, you might as well not do anything and let the search engine control the snippet… If you don’t use the meta description, the search engine will find the keyword searched for in your document, and automatically pick a string around that, which gives you a bolded word or two in the results page.