The Problem with Twitter
Twitter's been very well accepted by authors as a means to promote their books. Unfortunately, I see more than a few that seem to have lost the whole point of the system, and they devolve into the usual 'Buy my Book!' tweets that get instantly ignored. The problem here is that you can't treat something like Twitter as a traditional medium for advertising. It's not a one-way method of communication, it's a conversation, and if all you're bringing to the table is the kind of breathless begging for money that people see every day on TV, you won't get or deserve many followers. In a conversation, you can't expect people to stick around and listen if you're not saying anything worth hearing or anything really different from any other speaker.
Let's get into how to properly use Twitter to promote your book.
I honestly can't say how many authors I've seen who are clearly using some kind of automated system for tweeting. Their feed is mostly links with popular hashtags, or a regularly scheduled tweet saying 'Buy My Book!' Who's actually listening to that? They may have a thousand followers, but are any of them really taking notice? A certain level of automation is good, but not when it makes an author look like a robot who does nothing but beep on cue.
Authors have to mix it up. They have to actually be a part of the conversation. Talk to others, use hashtags wisely, and make it clear that you're listening and responding. So, an equal balance of retweets, links, quotes, @replys, and plain bare text is what's needed. You want people to value what you say and follow you because you're interesting, not because they want a follow in turn? Then you have to provide something worth reading.
Twitter is only 140 characters, but that's no excuse for writing only a few words. There is an art to composing a message that short, and it's a lot easier if you use it all. You can leave room for a retweet, but it's not worth betting on getting that retweet and cutting off precious characters as a result.
Text speak is also a big no-no. Authors are supposed to be trading on their ability to sell their writing. Any author who decides to scrap their spelling to get a message into only 140 characters instead of rewording it isn't doing themselves or their writing any favors.
If you reply to another tweet, and your reply starts with the @name of whoever you reply to, then your tweet will be hidden from anyone who doesn't follow both you and whoever you're speaking to. This is ostensibly to stop non-relevant conversations from cluttering up your dashboard, but it'll hamper part of your ability to make connections with people. Be careful how you structure your tweets.
Who to Follow
I don't follow anyone who isn't an author or aspiring to be an author, for example. I'm just not interested in what, say, accountants like to talk about. I also notice when someone who follows me is already following more than ten thousand other people. This pretty much means that they're following me in order to get another follow back, and it suggests that they're not really listening. Unless that person has some really great and insightful tweets, then I lose nothing by ignoring them.
The point of Twitter is not to get the most followers, or to follow the right people, or to spam links to an Amazon listing. It's about conversation, and connections, and building a circle of interested and interesting peers in the same area. Being personable is a far better way to get attention and sales than just shouting the same thing over and over.
For the record, I don't follow many people, but I listen to all of them.