Writing a good meta description involves a bit of skill. This is where the “art” part of SEO comes into play.
A meta description should primarily be written for humans, and secondarily for search engines. The title tag and meta description tag are the two things people will read to decide if they should click on the #1 or the #2, or even the #6 spot. Even though the #1 listed page may be more relevant according to search engines, if I don’t connect well with the meta description and what it says, I will click on a link further down.
A meta description should be no more than 150 characters, and be a relevant summary of the page itself. Think of it like what you would say in one tweet about the page. If you can repeat the description somewhere on the page, that’s good too.
Recently, Google has been creating the meta descriptions for websites automatically if they are missing, or if they simply think they can do a better job. Either way, you don’t want Google writing your meta descriptions for you, so try to come up with something relevant, and worthy of a click at the same time.