Google does factor a little to the META tag text in ranking a page, so you should definitely put attention to fill in this META tag on your web pages:
<meta name="Description" content="Your best sales pitch here" />
Google uses the first 160 characters or so (about 25 words) of your META "Description" tag to populate what is displayed under your listing on a search results page.
If no META Description tag content is found, Google uses the description from the DMOZ directory. If you don’t have a DMOZ directory listing, it uses semi-random snippets from your page that contains the search term queried for. This can lead to some really awful-sounding descriptions, as rarely does anyone write anything compelling in the META Description tag.
So take your best shot and come up with your best sales pitch in 25 words or less to put in your META Description tag. Something that would actually compel someone to click on YOUR listing. Descriptions that do well include a call to action ("visit us today"), phone number ("call xxx-xxxx for more information"), geographic term if applicable ("located in Seattle"), discounts, specials, prices, anything that will draw the eye and make them click. Basic direct marketing 101 pitch.
Note: If you want your META Description text to be used, it must include the exact phrase that was queried