There are actually two different places in your META Tags where information is collected.
Description: Make a good description of your site using descriptive words for your specific business in your specific area. Like I'm in Southern New Hampshire so I use stuff like - new hampshire, granite state, ice hockey, game schedules, event pictures, seacoast region, etc etc - They become items the search engine will give OUT when someone searches.
KeyWords: Keywords are what the search engines key in on. Make sure you DO NOT REPEAT key words a lot or the search engine will IGNORE them like spamming.
A good site for HTML and its underlying parts is:
http://www.htmlgoodies.com
Its where I learned my stuff.
Sarge