When it comes to social media, it can't be ignored as an effective marketing and promotion mechanism. I run into people who still eschew its value. They look at social media like Facebook and mistakenly believe that it's only good for reconnecting with old high school flames or playing Farmville. The real value of social media works likes this (and if you're not participating you are missing out on a huge opportunity):
Replacing the community newsletter or bulletin. In many ways social media like Twitter or Facebook have replaced the town crier. The news feed give equal access and lack censorship. I've often learned the headline news of the day on Facebook vs. the news. I don't like watching the news anyway, because it's so negative. On social media, you can read about the events as people react. You can also hear what is truly going on with your neighbors (if you're connected to them). While loaded with minutia, social media often provokes great discussion and debates among its participates.
Reaching your network. Facebook and Twitter enable you to reach out to your network. You can build your network to thousands of "followers" or "friends" and then you have access to reach them via your ability to post announcements.
Making it personal. Facebook also enables you to create a real "persona," so your prospective business or clients can actually get to you know you before they do business with you. They can friend you and then watch what you post; how you behave online; and assess whether or not you are someone they would want to do business with in the future.
Keeping your audience informed. You can use social media to keep your community updated and informed about your business, products or services. Avoid, though, making it like an advertisement. Instead, make it fun and interesting. I keep people informed about a book's progress while in production. I provide pithy but interesting updates. I let people know what I'm working on. By sharing this kind of information, it incites interest in the book and builds anticipation for when it's released. You can also create "Events" and then invite your social media community to attend.
If you're not using social media, you are behind the wave of modern marketing and promotion. It is the grassroots way to do outreach directly to your target market. And its main cost is time and effort to maintain.
Tip: If you want to stay at the top of people's news feeds on Facebook, make sure you post at least twice a day.