Think of your meta description tag as Google Adwords ad text. The purpose of this description is to entice searchers to click the link. But you can also use it to gain leads and sales directly by adding a phone number for example. As with Adwords ad text, you have a limited amount of space. Use keywords to help make the connection between the most likely used search phrases and your link, as these will be bolded if they match the search query. But most of all, use the description to entice searches into clicking your link.