The content of your website is as important as your title tag and optimising the content and the keyword density is one of the best things you can do to improve search engine ranking. Search engines love text so if you can, try to create pages with lots of text and don't forget to include your important keyword phrases. In general try to have between 100 and 250 words on every page you submit to the engines. This amount of words will also help the search engines understand what the page is all about and your site will have an advantage over other sites with less content when it comes to ranking.

Another very important concept is keyword density. What is keyword density? Basically it's the ratio of the search phrase to the total number of words in the page. Again you want to focus on your most important keyword phrases and have a keyword density ratio of around 5%. There are many keyword density tools out there which can help you determine keyword density on your site and can help improve keyword density ratios.

Keep in mind that search engines calculate keyword density ratios differenty. Google for example does not include the metatag when calculating the ratio but other search engines such as inktomi powered engines do inlcude metatags.

Keyword Density.com: Keyword density and word depth calculator
Keyword Density: SEO Tools