People tend to use different keyword density schemes and percentages in order to rank higher in a search engine. The problem is that the result is usually a SEO copy of a text that is not at all attractive and this does not actually help rankings. In addition, it will irritate website readers and cause even more problems.
In order to improve your rankings it is much better to use combinations of the most important keywords that you are optimizing your content for. This is going to increase the chance to rank for different combinations or similar terms and the text quality is not at all going to be affected negatively.
The technique mentioned above will increase important term keyword densities without you even realizing it. The main goal is not to end up increasing this density but to put in text that includes those words that are most likely going to be used when the potential visitors do a Google search. We recommend that you use the Keyword Analyzer tool to check KeywordRank. This is a much better metric that is going to help as it takes into account many parameters like usage, relevancy and keyword positioning.