Social media play a very important role nowadays. So here are some tips for you:
1. Create accounts on all major social networks: Facebook, Twitter, Google+, you can also create a company on Linkedin but it depends on your niche.
2. Share useful information on all these accounts. But mind that you should create different messages for each network as their audiences differ.
3. If you sell products, consider creating promotion: you can give customers discounts for liking you on FB or G+ or for tweeting about you. This extension for Magento can give you a clue http://amasty.com/facebook-twitter-promo.html
4. If you have free products, consider giving them for FB likes (like that http://amasty.com/magento-facebook-like-to-download.html
5. If customers can create accounts on your site, you can let the login and register with their social profiles. Here is an extension for that http://amasty.com/magento-quick-ajax-login.html
and here you will find some useful tips about social login http://blog.amasty.com/5-tips-to-use-social-login-like-a-champ/
Follow these steps and create good social communities around your brand.
Hope that helps!