As the writer of SEO friendly content you have two different objectives. To create material that uses your keywords enough to make Google rank it highly but not too much that it thinks your content is spam. At the same time you need to provide content that the human visitors to your site want to read. The key to this is balance and you can only learn this by doing it. There are tools that help you pick good keywords, templates that help your SEO with Keywords and Headings, rules of thumb that guide you to the Ideal Amount of Keywords and tricks like Double Dipping to give you that extra little bit of traffic. However no one can tell you what you need to write because SEO Content Writing is a craft that can only be learnt by experience.
Chris Tregenza runs a variety of web sites including MiceLife, writes free seo articles and a SEO Blog
Better search engine placement through article writing.