Best Practice (Good)
Rather than focusing on keyword density, spend time creating quality content that will satisfy user search queries. Insert keywords only in high value locations, such as H1 tags and page title tags.
Typical Practice (Bad)
Focus on highly detailed keyword analysis and insert high-value keywords into page content, monitoring keyword density, in order to produce higher search engine result page (SERP) rankings.
Benefits: Modern page ranking algorithms rank pages on a variety of factors and place less focus on keyword density and more weight on quality content, page authority (quality links to your page on external sites) and semantic markup. Pages can actually be penalized for absurdly high keyword density and other "black hat" techniques that were once the norm.