Meta Descriptions Made Easy

Meta Descriptions do not improve or add to the search engine optimisation of your site. Meta Descriptions won't affect the position of your page in the SERPs for your keywords.
The Meta description is a fragment of HTML code that belongs inside the "head" section of a Web page. It usually is placed after the Title tag and before the Meta keywords tag, although the order is not imperative.
If you don’t have certain keywords in your meta description tag, and those keywords are searched by users on Google, the first text on your site will appear in the description of your URL on the Google Search Engine Results Pages (SERPS).If the keyword is valid to your web-site, you may consider adjusting your meta descriptions, as well as website content, to reflect this keyword. This may not improve your SERPS ranking, but it will improve the content of the descriptions of your website on Google’s SERPS.
It is clear that more control you have over your record in the SERPs, the more click-throughs you should have. If the description of your web-site catches attention and creates interest in your website, than the likelihood of users clicking through to that site increases. If your Meta description tags can help with that, then it's definitely worth the time to create persuasive, keyword-rich Meta descriptions.

You should limit your Meta description to between 170 characters or 200 characters at most. The style should be consistent and the information should be relevant to the content of your website.
For more information on making your site relevant to Google and usable to people, visit Web-Smart.