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When writing an article there are some very basic points to keep mind

1> Shortlist of 2-3 keywords which is your target set. It should be somewhat around 3-5% of the entire article. Don't overuse it, as search engines are quite smart on this & can negatively impact website in long run.

2> Anchor Texts-Generally in articles/posts you can put at max 1-3 linkback to your website. While linking always try to use your most competitive keywords in the anchor texts for getting links.
The basic reason for this is targeting these keywords for your ad campaigns will cost you more but in case of articles/posts your not incurring any costs.

3> The End Objective - Be clear about the intention of writing it. Like some maybe for increasing the sales or some maybe for just to get traffic.

NOTE: All articles should be not always be a sales targeted or always talking of a product.
Some articles should be written as like providing useful information,or "How To Do" . If that is done many people will use that as a reference in blogs or forum posts, in turn increasing visibility of the site in long run. It is often called "Linkbaiting" or "the natural way of quality link building" . But quality links gathered through unique content on the site is also good for websites.

4>Don't forget to include a detailed Bio -It should not be too long, but it needs to include your important keyword phrase within the text links, which will link back to your Web site. Make sure your Bio reads well and realize that it must be kept down to about 300 to 400 characters. Some editors just don't want your Bio going on for miles.
Reference
http://en.wikipedia.org/wiki/Methods_of_website_linking
http://www.jimwestergren.com/link-bait/
http://www.mattcutts.com/blog/seo-advice-linkbait-and-linkbaiting/