Your goal: to promote yourself and build your personal and professional brand online. You’ve joined Facebook, Twitter and LinkedIn – and, just to cover your bases, YouTube, Flickr, Posterous and Foursquare, not to mention your blog. But just being on these sites isn’t enough to turn you into an online sensation overnight. Like anything worth having, it requires some work on your part – and the best place to start is with your bio. Your social media bio is a critical component of your personal branding toolbox. It’s the first thing people will read to find out if they should follow you, friend you or do business with you. According to Hubspot, almost two-thirds of Twitter users don’t have bios on their profiles.