In 2003, Delicious (then called del.icio.us) was founded and coined the term social bookmarking. Even though the concept had been around for some time, Delicious pioneered the concept of tagging the links allowing for easy categorization of your bookmarks.
If you aren't familiar with the idea of social bookmarking you might be familiar with some of the websites that provide this service.
Today, arguably the most popular social bookmarking site is Pinterest. But, historically, depending on the audience, others that have been (and continue to be) popular include StumbleUpon, Digg and Reddit.
A social bookmarking site is a website that doesn't contain it's own content. Instead, it contains links to other content on the internet. Consider that the most common use for Pinterest is to pin a picture (link) from another website and then your followers will be able to click through to see that link.
Social bookmarking allows you to get your content out to multiple audiences in multiple ways. Depending on the type of post and the audience your bookmark is submitted to, you will find that different social media platforms (including social bookmarking sites) will generate different levels of traffic. Moreover, other people will re-post your links if they really like it at different rates depending on the platform.
As you consider social bookmarking for increasing your traffic and SEO, you'll want to make sure that you don't avoid the more mainstream social networks such as Twitter and Facebook. You'll likely still get more traffic from those sources so don't forget about them.
When you are submitting pages of your website to social bookmarking websites you want to make sure that you keep everything relevant. Don’t submit every page of your website to Digg or spam irrelevant links to Reddit. The best way to utilize social bookmarking sites is to utilize relevant content on your website. Say you have a blog post that is about home renovations; you could submit this to the “Home Improvement” category of StumbleUpon, or to a relevant subreddit (a subreddit is a category in Reddit) that focuses around home improvements or DIY projects.
Social bookmarking communities are very good about self-moderation. If you are pushing irrelevant content, your link will likely get deleted and your profile may be banned from posting. However, these websites have a plenty of traffic coming to them and, if the content is truly relevant, odds are it will get upvoted, shared, repinned, etc. This will bring a significant number of relevant users to your website.
Take 5 minutes and do some research as to which website(s) would be the best target for your social bookmarking efforts.