Ideally, we should focus on the content which has been written without worrying about any keyword for which you are trying to optimize. But as SEO we have to adjust t he keywords and have to maintain the good ratio of keywords in the content. Three ways you can optimize it.
Keyword Density : it is the ratio of our targeted keywords to total no. of keywords in the content. Do not exceed it up to 3 to 4 %
Keyword Proximity : Position of the keywords. It is very old concept where we were try to add the keywords at specific position on the page in footer, header,url etc.. and it still works.
Keyword Prominence : There is not any standard available to measure its prominence. You have to analyze carefully the relevancy of the different keywords used in the content.