SEO --- keyword selection

the rank a search service assigning to a website has nothing to do with the keywords extracted from the website.

As far as keyword's selection is concerned, a good keyword selection should consider the following two facts.

1) the popularity of keyword, whether it is a word used by searchers in a very high frequency.
2)Competitiveness, How many other pages target your keywords? Should you have more specific keywords?

The goal is that a search could find the given items easier through the concerned search services.

References

http://www-128.ibm.com/developerworks/web/library/wa-seo2/