The SEO field is comprised of both on site and off site SEO. This division in the Google algorithm is hypothesized to be about 25% on site and 75% off site.
The on site factor is comprised almost entirely of link building. There are many ways to build links such as: blog comments, directories, social bookmarking and article submission.
An article submission is one of the most effective and efficient of these techniques. A single article can get your site thirty or more links.
First off it is important to write about something related to your business or the business of your client. For example if your client is Toysrus you should not write about Toysrus, but write about the toy industry (a.k.a. no self promotion).
An article should be around 700 words and follow grammatical rules. It is also very important that your article does not resemble spam, this means avoid using any word over 20 times.
It is difficult to submit articles on your own so look for a business that you can sign up with that will submit your articles to related sites for you. Depending on what category your article fits in, it will be submitted to a couple hundred to a few thousand sites. Some of these sites will accept and publish your article. You probably will not get links out all the sites that publish your article because google will not index all of them.
Its important to include a variety of link building techniques in your off site SEO. Article submission is a great way to get several links in an hour or less.