Article standards developed by SEO experts are a word count of 400-500 words per article and a keyword density of approximately 2%-3%. Writing standards prohibit keyword stuffing, so articles are reader friendly for humans and not just crawlers.
Article submission sites allow link backs to your website. These link backs should be keyword optimized using HREF tags with keywords in the title tag.
Although common SEO methods specify that duplicate content penalizes a website ranking. You should submit to Articles Directories only unique (non duplicate) content.
