I want you to check out an excellent study by Ian Lurie on the quality of Twitter followers. He started collecting data after some spammy guy who had 32,000 followers retweeted one of his posts. You might expect that a retweet by a person with such a huge following will grant your URL lots of clicks and further retweets. Well, what Ian got was only three clicks.

I won't tell you the rest of the story, for it is too cool to be rewritten. Twitter power is not about the quantity of your followers, but about the quality of your, and your followers, content. In this part of my guide I will teach you how to gain quality followers.
 
Think: Yeah, that is my first tip. But I think it's the most powerful one. Think of the way YOU follow new people and think how many of them eventually stay in your Twitter feed. Then do the same stuff that they did to get followed by you. If you ask me I mostly follow people who blog. When I see a smart post, I will do my best to find the author on Twitter, follow him and perhaps even communicate a bit. The second way I may follow people is when they @-mention me in their tweet. I will usually check the profile of that person and if it appeals to me – I'll follow them.
 
Follow to get followers: This is the best known tactic to grow your follower count and it's based on the newest psychological disorder called ISFBaG (I Should Follow Back Guilt). When you follow someone, they receive an e-mail notification and may follow you back. You can mass-follow people via Twitter interface, use some online tools or even create scripts, which will auto follow people, who tweet specific keywords.

Another study by Hubspot shows that your following to followers ratio dramatically affects your chances to get a follow back. So ideally you need to keep the number of people you follow lower than the number of your followers – this way you are more likely to get a follow back.

People might think that having a large number of followers will add credibility to their account. Well from now on they won't be able to trick you! It's easy to measure the credibility of a Twitter account by comparing the number of followers to the number of the lists.
 
Rand from SEOmoz has one listing per 7.6 followers ( 24,368 followers / 3,187 lists = 7.6).
If the ratio is more than 10 – that's a signal that a person is a spammer who does a lot of mass-following.

Run a contest: People love contests, freebies – such events always attracts great attention. Classical contests go well on social networks, but if you can think of some extremely unique event, it may do wonders to your social presence. There is an interesting story, I would like to share (little NSFW) how Dutch porn star attracted a lot of people to follow her! She got around 15,000 followers within a couple of days since that claim, but you should think twice before running a contest like that. :)

Know who is sharing your content: Once you publish some content online try to track who is tweeting about it. You already know that those people appreciate your work, so it's usually a matter of a "thank you" message to get a follow back from them.
 
Promote your Twitter account: That's probably the most popular and most obvious advice, so I've left till last. Use your Twitter account URL everywhere you can: e-mail signatures, social media profiles, forum signatures, blog comments, business cards etc. There's no rocket science here, just use every opportunity you can to share your Twitter account.

It's cool to have a couple thousand followers, but do they care about you after all? You might have followed my tips to gain quality followers, but still it does not mean that they will interact with you and help you to spread your content. What you need is to build relationships with them so that they know who you are and read your updates.

Reward your followers: You can do that with a follow back or, alternatively, you can just thank them for following you in a reply or direct message. Just don't spam everyone with those automatic Direct Messages which no one cares about. Try sending a personalized message with some information that the recipient may be interested in.

Retweet others: People on Twitter usually keep an eye on their retweets. So try retweeting someone else's tweet and add a personal comment to it – this is a great way to get noticed and start communicating with people that you follow, and your own followers.
 
Public mentions: #FollowFriday or #ff is a nice occasion to show your appreciation to someone by publicly mentioning their account and providing a reason for others to follow them. However there is no need to wait till Friday to do that.
 
Twitter lists: When you add someone to a Twitter list, they won't be notified about it, but they may find it out on their own sooner or later. Make respectful Twitter list names to show some appreciation to people you list there. I am really happy each time someone adds me to a marketing related list. (this was a call-to-action :) )
By following other people's Twitter lists you can get some attention too, as people might check who else is following their lists.
 
Twitter list Ninja Tip #1: follow @listwatcher as it will send you a DM each time someone adds, removes you from their list, or changes their list. Being listed is a reason to get in touch and say thank you, ( or something else, if you were removed :) )
Twitter list Ninja Tip #2: learn how to automate your lists with Formulists online service.
 
Follow people who @mention you: This is a great way to show your appreciation for being mentioned and, besides, this will make a person to take a closer look at your profile and what you tweet about.
 
Twitter Favourites: Currently this feature is not widely used, but I think it can be considered as a form of appreciation too. Each tweet that you add to your Twitter favourites is saved in your profile under the "Favourites" tab. I doubt that the author of a tweet will ever see that, but others might find your favourites feed useful and that can be another reason to follow you.
 
TweetChats: It's a regularly scheduled online event which is perfect for networking. For instance you can check #seochat – this is a search marketing chat which is held every week. If you fail to find a TweetChat on your topic, maybe you should launch one yourself.