What is Social Bookmarking?
Social Bookmarking allows people to bookmark their favorite sites, and associate “tags” or words with them so they can be easily recalled in the future. Other people can also look at the sites you’ve bookmarked, and they can also bookmark them.

Due to its social nature, it’s a very powerful tool for SEO. That’s why the quality of your articles are very important. Provide useful, free information that people would want to remember your pages for. Avoid sales talk, and focus on what the readers would be interested in. Think of things from the reader perspective. Why would they be interested? Why would they keep reading on?

Quality Articles
Write quality articles on your site, and bookmark them on Social Bookmarking sites such as DIGG, Delicious, Technorati, and etc. Ask your friends to bookmark these sites as well. The more exposure your articles get and the more useful they are to people, then the more chances those people will bookmark your site.

SocialMarker.com
One free tool you can use to easily bookmark your sites in dozens of Social Bookmarking sites in only a couple of minutes is SocialMarker. It helps to automatically fill in the fields, makes the sign-up and log-in process easier, and automatically moves from one Social Bookmarking site to the next.

AutoPoster
Another tool that can help you bookmark your sites semi-automatically is Autoposter.

ShareThis
Place ShareThis button on your website page or blog to easily allow users to bookmark their sites on their favorite social bookmarking websites.