Keyword research is a necessity for doing business online. The best site in the world needs to have decent keywords, or it won't be found. If fishing enthusiasts are searching for "fishing," they'll never find your site on "angling." However, maybe you can't compete with "fishing" either. Too many quality sites are already in the search engine results. How do you find keywords that will get you that traffic?
Optimization experts advise comparing demand to supply to find good keywords for your web pages. My experience, though, is that many of my pages with "good ratio" keywords never show up in search engine results, while others that I shouldn't be able to compete with, are right there on the first page of results. This is because it isn't just quantity, but the quality of the competition that matters. Supply/demand ratios just don't give the information necessary.
Better Keyword Research
Here is a better and easier way to do your keyword research. First, Find keywords at the Yahoo site (formerly Overture): http://searchmarketing.yahoo.com/rc/srch . Click on "Keyword Selector Tool," to see how much traffic a keyword phrase had last month. Get together a list of words and phrase with decent demand. This depends on the nature of your site, but for my own sites, I won't optimise a a page for a keyword with less than a few hundred searches per month.
Next, go to http://toolbar.google.com , and install the free Google toolbar on your browser. With this you can see the "pagerank" of any web page. This is a ranking between 0 and 10 that Google uses to help determine which sites show up in the results when a search is done. See what ranking your own pages have. This tells you (roughly) how well you can compete against other pages for given terms, assuming you are doing okay with your on-page optimization too.
This also is a guide to the page rank you can get on any new pages you create. If you have a pagerank of three on several of your site's internal pages, you can probably have the same (with a little time) on new pages. You do this by internally linking to the new pages, especially from the homepage and site map, as well as from any other relevant pages.
To complete your keyword research, type your potential keywords one by one, into Google or another search engine. Click through to the pages in the first ten results, and note the pagerank of each. If a couple of them have a page rank that is lower than that of your existing pages, you can probably compete on that keyword phrase. Create pages that are optimized for these keywords.
If the first ten results have a page rank of 5 or higher, and your own pages are 3, you can't compete (yet). Sometimes you'll search keywords with 3,000 searches per month, and 300,000 results, yet the first ten results will have pageranks of 2 and 3. Others with 30,000 searches and 10,000 results will have only pagerank 5 or higher results. Obviously, demand/supply ratios are not all that matters. This is a better way to do keyword research.