Facebook can be either the best way to grow your writing career or the biggest waste of marketing time, depending on how you use it. Writers constantly give up on Facebook, moaning about the fact that they got very few sales from spending their valuable time there. When done right, Facebook can be an important part of a long-term writing career plan, one that can help your entire catalog sell instead of just one book.
It's Social Media, Duh!
No one goes on Facebook looking for ads or a hard sell. In fact, most people unfriend or hide people who spend all their time trying to sell them something. Using social media is a lot more subtle than that. Facebook is so established that it has habits and manners of its own, like many other social situations, and the first one is that you're on there to be social. To pass the time in a fun, funny, or pleasant way. Maybe to learn a tiny fact, but never to get a hard sell.
Branding is Key
You may feel like a massive sellout talking about branding yourself, but that's just the name that describes what every single author does in trying to sell her books. Getting people to know your name, and trying to link your name with your book genre, is what book branding is all about. Let the fans discover you instead of putting yourself in their face. Make interesting comments on other posts in your genre. Make shareable posts about similar works, or topics that relate to your work. Always keep in the mix of people posting about your topic, be it romance novels or gardening books.
Making Friends
Of course, a friend on Facebook is completely different than a friend in the 3D world. Some people have tens of thousands of friends on the site, and those are the ones you want to cultivate. Use the hashtag (#) in a search to find those interested in your niche. Look on each person's personal page to find out how many friends she has. Once you find one with a lot of friends, send her a friend request. A lot of people with huge friend lists will automatically accept friend requests, simply to increase their friend score. This is a huge win if you can post something they want to repost, as they'll be advertising to their entire friend list for you.
Be Yourself
It's too hard to keep up a persona for months and years. If you're naturally snarky, be snarky in all your posts. You'll turn off some fans, but you'll find others who love you for it, and those will be rabid fans. If you're a mom type, a nerd, a fashionista, or a jock, let your personality shine through every post you make. You'll connect with your fans in a solid way.
Keep the Faith and may the Force be with You!