The Description tag - It should be about 140 characters total or around 20 words.
Make sure to include your keywords from your title tag and your optimized keywords for your page - but don't spam! Don't repeat your keywords more than twice! Google will see this as spamming! You will loose position and ranking and validity in the eyes of Google by spamming.
Let's look at this realistically for a moment or two. We may not want to admit it, but not being in Google's good graces can cost you these days. They are the search engine. No other search engine really matters. Phrases have popped up and have made Google the giant they are. If you need an answer, you can Google for it. Want to check out your ex's current exploits? Google your ex's name but in some places we might consider this stalking, let alone a bit nutty. Need to look at an applicant's history? Just Google your applicant's name and you might not hire them. The fact that the name Google has become synonymous with searching the web for information should in it self explain the importance of Google being able to see, grade, rank and show off your site. So don't piss off Google.
It is easy upset Google and break what might be one of the best relationships you might set up on line. Just spam keywords and see how fast your rankings drop, but keep something in mind. Using a word more than twice can be considered spamming in your sites keywords so the word "news" could be listed in your keywords as follows: "News, news," . Using variations is helpful.
Keep in mind, successful webmasters will make their descriptions stand out from the crowd. They will entice the surfer to click their link. To come to there site and have a look around. As I stated before, it is also the first contact with your potential visitor or prospect so it is imperative to make a good first impression.
Take a minute and go on Google. Run a search for anything you want. Read the top 10 search returns descriptions to yourself. Now go to the last page or so of your search results and read the descriptions. Now if you did a search on something general like "news" you probably have a search return of about 3,340,000,000.
First off this should be a clue that this is a heavily used keyword. It probably wont garner much traffic to you and will more than likely be of little service for you or your site by itself. Second off you will notice that in the first 10 results you will see well written and decisive reasons why you should click on those pages. The bait covers the hook well. It has been designed to capture the searchers interest. If you are truly looking for "news" and you have a reason to click more than likely you will click on something on this first page. You may not stop there but more than likely you will click on something on the first page. Admit it, we are a fast food society, its ok, we want our fries and a shake and we want it right now. Not in 30 or so seconds but right now. We have other things to do in the day. Let's get it over with already.
Put yourself in the searchers place, you need to know something, you searched for it, you're going to click something. It's like the old used car lot, you wandered in there to look around and kill time, but you wouldn't mind getting a newer car. The salesman asks you if he can help you and without hesitation you say "nope, just looking." We call that a conditioned response. You didn't think about it, you just did it. You have been conditioned to do it over years of doing it, and you will continue to do it.
The good news, he or she knew you were going to say that. Any salesman that has been in the business for more than 6 months has learned and become conditioned for the knee jerk response of "nope, just looking'. The smart ones learn not to ask "Can I help ya?" Why? Having a different approach takes the customers guard down for a moment. It separates the salesman who can make a comfortable living in sales from the pack of wolves that the customers have run into in the past. Remember, you only have one chance at making a first impression. And it takes less than a second to make that first impression, so make it a good one.