Meta description tags are like a permanent 'Tweet' for your website when it appears in search results. The 3 majors SE's have different character limits but if you go with the shortest (google at 160) you are talking about a defining 'tweet' like statement that will be the first bit of info a prospective site visitor reads. You of course want to include prominent keywords and make the 160 character blurb as sexy as possible while also providing that concise message that spells out the site content efficiently. In sales, this would be called the 'elevator pitch', something that sales pros and networking job seekers practice and hope to perfect. A pithy, memorable introduction that can be smoothly spoken in about 60 seconds. How do you approach your web-sites Search Engine elevator pitch?