Always make sure to place your most important keyword at the very beginning of the Content of the page.
Never stuff your keywords to the bottom of the page cause this will drop your keyword prominence significally.
It refers to the percentage of keywords that can be found in the indexable text on a web page.
To find the keyword density, use the formula:
density = (keyword repetitions
/ total words)
We should maintain at least 2 to 4 % and not exceed 5.5 %.
To check your website statistics, visit http://www.ranks.nl/cgi-bin/ranksnl/spider/spider.cgi?lang=