I'd love to write a long, helpful post on this right now, but I don't have the knowledge nor the time. What I do have is an article I just read and a theory.
Don't read it all because it's not spot-on and sort of long-winded, but it's interesting to get the perspective. (For two much more useful articles that I say you MUST read, scroll down to the Further Reading part of this post.) The thing that did it for me was in the last line.
In the end it's all about stats: the hidden ones and the real ones. If you're writing and trying to self-sell and net-promote, do your own stats. Calculate your investment of time and money in writing versus social media. Do you want to spend 80% of 80% of your time Facebooking about cats in the hope that you'll make a 2.12% increase in sales on a book you had to write in 18 days? Do you want to spend 80% of your time creating unpaid market propaganda for the social media industry?
Or would you rather step away from the hype altogether and spend as much time as you can being a 100% writer?
Some things in the comments were more useful, though. Using a tool such as Twitter is not about linking your book 3 times a day. It's about connecting with potential readers, or possibly people who are reading your work. If you use Twitter to shove your book 3 times a day, people will get tired of you, and the thing is, people just don't click on those links that much.
My book isn't available yet, so I haven't even had the chance to link anything. But I promise you, just thanks to the title in my profile description, I've had people showing interest, asking for me to let them know when the book is out.
And hopefully they'll love it.
My theory? Write good books with good titles and good blurbs. Even better, write better books with better titles and better blurbs. Get more stuff out there. Devote your time to writing. Write novels, and in between, write shorts and novelettes. The more you have out there, the more people can read if they like your work, and they'll be even more likely to talk about you.
Use Twitter and Facebook to update your progress, but don't over-market. Maybe link it a couple of times once it's out. If people have shown interest, let them know. Apart from that, be friendly. If people ask about the book, let them know about it. Stay calm.
Send the book to some reviewers (look up blogs that review your genre or price) to give it a start, mention it on your blog, then forget about everything and write the next project. Update Twitter and Facebook a couple of times a week with your progress -- say, every time you finish a chapter, or a few chapters -- and apart from that, retweet or comment on the Tweets that connect with you.
Getting Focused Followers on Twitter
I write fantasy, particularly high/epic fantasy. So to get followers who might be interested in what I write, I follow people who follow authors who write in a similar genre. So I would go to Christopher Paolini's profile, click "followers", and then go down the list, following around 50 people, for example (aiming for English speakers), and then move on to George R. R. Martin's profile and do the same.
A few days later, I'd use "ManageFlitter" to unfollow the people who didn't follow back, so I don't hit the wall of Twitter's "ratio" system.
Focus on the writing! Remember that books take months to find their wings, but once they do, they'll hopefully keep flying. Word of mouth grows exponentially, but it takes time for your book to get started, so give it a bit of a push at the start. Interact with your readers when you can.
And the more work you have out there, the better. (But make it good.)
I found these articles today. It would be in your best interests to check them out!
The first one discusses how to work Amazon's algorithms with an emphasis on the initial push.
Social media doesn't sell books (In a way, it does -- read the next article to find out how.)
This one discusses with 3 "prominent" authors how effective they think social media is, and how to use it effectively. That is, by being "social" (meeting people and being down to earth), only "promoting" when you have free promotions, and having a web presence (getting interviewed on blogs, simply being there on Twitter and Facebook).
DOES SOCIAL NETWORKING REALLY SELL BOOKS?