in my opinion, If you want to get a lot of free SEO traffic then it is best to optimize your site for one particular keyword phrase. make sure that the keyword you are targeting is not too competitive but at the same time gets lots of daily searches.
1. To find out how competitive the phrase is, go to Google.com and type in the phrase with quotes (i.e. "keyword phrase") and see how many competing sites there are. The more sites, the harder it will be to get free SEO traffic. Anything under 100,000 is not too competitive.
2. To find out how many monthly searches a keyword phrase gets, use the free Google Keyword Tool. When you do a report for your keyword, it will reveal how many monthly searches it gets. You'd want to make sure that your keyword phrase is getting at least a few thousand searches per month to make it worthwhile.
Once you have done all the above (what they call on-page optimization), you then need to get quality backlinks to your site for it to rank well in the search engines. Look for websites that have a high page rank that you can leave your links on like article directories, blogs, forums and web 2.0 sites (e.g. Squidoo).
Make sure that you link back to your site with your keyword phrase as the anchor text.
Do this on a consistent basis and before long you'll have a heap of backlinks, great search engine position, and a lot of free traffic!
Hope this helps
