Decide what defines you.
What should people know about you? What is the primary information you want people to be aware of? Maybe it's just the basics, or your professional experience, or a hobby. Figure out how you want to be represented, and make sure everything you do online reinforces how you want to be known.
Embrace the Big Three.
200 million professionals are on LinkedIn, and presents a clean, well-organized profile that says you're savvy about self-presentation. Twitter and Facebook profiles can also align with your communication goals. These three services are key to establishing and controlling your net presence.
Explore other options.
Invest some time in developing yourself on other (respectable) sites; you can join a professional networking group, or build up your hobbies on a number of sites, like Goodreads, Ravelry, or Steepster.
Set up your site.
Lastly, set up your own site: it's easy, cheap, and effective to buy your own Web domain. And it’s even simpler to point a blog you establish to that domain name. Update your site from time to time-- keep it fresh with content that you've curated about yourself and your interests.