It really depends on the search engine & what the person is looking for. For example, on Google & Yahoo, if I type in horse coverage, a web site that I did pops up -
www.horsecoverage.com but on altavista.com - it does not even show up on the first two pages.
You do not want to repeat your keywords, but you do want to have as many of your keywords in your meta description as possible. If you exachenge links with a few web sites - that will also put on more on top with some search engines.
Check out this site to see what is being searched:
http://www.keywordcity.com/
And also read this site - it helps to answer the basic questions:
http://www.searchenginewatch.com/webmasters/index.html
Corey