The SEO On Page optimization is very important for SERP (search engine results page) and PR (page ranking). Your keywords 
need to be in the URL and post titles and you also need to include related keywords that flow naturally throughout your posts. Good content with proper keywords will help drive more related traffic to your site and help rank for related keywords and your main keywords. This strategy will help to build authority for your site and better ranking with the search engines. This is a very important point you need to understand when developing your site, each related keyword will strengthen your main keyword, which helps your overall site value and PR. So as you develop authority for related keywords they in turn help build authority for your main keyword. They all play together to improve your SERP and your PR. On page SEO needs to be done very thoroughly before you start on Off Page SEO or link building efforts. You can rank very well with the search engines by developing your site with proper keyword strategies. Be sure to pick keywords you can compete and rank well for. Then write good content posts for each related keyword. Use Google Adwords: Keyword Tool to find all the related keywords to your main keyword. These related keywords usually have more words and are therefore called long tail keywords. Long tail keywords are better defined searches and therefore have better conversion rates than short tailed or broad and very competitive keywords. The longer the tail the more likely a conversion. So it makes good sense to rank well for the longer tail keywords that convert better.
The Learn Internet Marketing Tools website has some addition information you might find useful.