1.Easy Sharing
2.Keyword Research
3.Analytics and Tracking
4.Social Media
Sites like Twitter, Flickr and Facebook and now Google+ are going to be good avenues to expose your site and get people to notice your brand.
Social networks are also the golden goose for brand reputation management these days and for connecting with new audience.
Knowing where your traffic is coming from and how your audience behaves, will help you shape your site into something that more people will want to visit.
One of the most important things you can do to improve SEO is to research your keywords extensively.