If you're writing articles with the use of keywords to increase your online presence, it's not really a good idea to overdo it or do less with the use of important search engine keywords. It requires a certain strategy so that you won't come up with an article stuffed with random keywords. The density and placement of keywords is very important to optimize your articles for search engines. 

Search engine spiders scan a web page in such a way that it's important to place keywords where they will be easily detected and recognized as a keyword - so that your article will come up when someone searches for that specific keyword. A keyword is a word that is going to be placed in your articles for several times. When a search engine spider noticed that you have a word placed several times in an article, it will assess whether your page can be useful to users who look for that specific keyword. 

Although placing keywords on your article is very useful to increase online visibility, you should be wary of over-optimizing your articles for specific keywords. When you place a lot of keywords (keyword stuffing) in an article, the spider will detect that you're trying to trick it into placing your article in the highest position in search engines, penalizing your website for doing such thing. 

This will also greatly affect your page ranking and you might even get blacklisted from a particular search engine. If you don't want this to happen, do not stuff your article with keywords. 

Keyword density is the number of times you place the keyword in an article. Most people use percentage to determine how many times they will put the keyword in the article. Let's say, if you have a 100 word article and you want to achieve a keyword density of 5%, you will need to have the keyword placed 5 times in your article. 

There are lots of resources and guides recommending a keyword density over another but the most important thing is to understand the profitability over a keyword density in an article. Web-masters think in a different way - especially in the issue of keyword densities. As long as you don't over-optimize your article, you don't have to worry about being blacklisted on a search engine. You can make the most out of your high ranking and earn sufficient profit from it. 

No matter what keyword density you choose, it is important to place your keywords at an hourglass form - this means, there are more keywords at the beginning and the end of the article than the body. You must have the right keyword density for your article and make money from it as your online visibility grows.