I use social media (mostly Facebook) to promote my business (3L Publishing, www.3LPublishing.com) every day. I have been asked about way to promote books (and businesses) using social media. I am honestly good at some of the tips I'm going to give you and some others not so much. The following are my tips to use effectively use social media to market and promote either your book or business (it works the same):
Marketing Tools Connected to Your Social Media: If you have a website, newsletter, blog or Blogtalk Radio show, make sure the social media icons are connected to them. Every e-marketing tool you have should connect to your social media. I call this "interconnected and leveraged" marketing. Each marketing piece ties to social media, and each part drives traffic to the other. Think of it like a circular current or round-about with entrances to invite more traffic. This interconnection of tools invites interest and generates an audience for everything you're doing.
Profile Pictures: I have some very specific ideas about profile pictures vs. wall backgrounds. People like to connect to people ... not places. So I recommend you keep your profile picture a person not a place and your wall background a place or idea or concept. My personal pet peeve is talking to a social media "place" vs. person. I just don't know who I am sharing with. I don't like it. And you're less likely to form those important bonds with "places" and build relationships. Make your wall background the marketing device (use collateral and images for its background if you like).
Community: one word here: participation. Get out on the News Feed and participate and comment. I fall short in this respect. I am sometimes more active than other times. People who are active in their social media communities raise visibility. Raised visibility increases interest and increased interest generate sales (e.g., book sales). I know one author who is aggressive in her community, and she's enjoyed some great opening book sales. You can't focus solely on your wall activities. Get out of your little social media world and join the greater world at large.
Consistency: don't be absent. You have to designate specific time to actively participate in social media. I try and go online twice a day: morning and evening. Warning: don't get sucked into either. Limit your time. Try 15 minutes in the morning and 15 minutes at night. You don't want to get stuck in what I call the "social media vortex" and never get out. You can waste too much time when you need to work. I get asked all of the time how I do everything. The answer: limits. Limits are like moderation. Everything within limits works.