Well article marketing is one of the best marketing strategies to build the quality back links as well as to increase the keyword rankings that we often use in author's resource box. Articles are helpful in getting traffic. One thing is very important and that is post you article in the best and more popular sites like hubpages, squidoo etc to get back links from 8 page ranked web sites. If you post your article in multiple article directories Google will only index the first web site that will accept your article first. Some say that avoid duplicate posting and some say avoid spun contents and some say that you can post the similar article in to not more than 10 article web sites. So it is up to you whom you follow. Try to write a unique and relevant article to your web site and post them in to well ranked web site to get maximum exposure. Include your main keywords in the article and try to be relevant to the topic and try to give the readers a new article every time you start writing article.