There are 3 types of people that get 1000's upon 1000's of followers on Twitter.

1) Celebrities - Celebs get followers because of their already high media visibility and established fan base, people just love them, so they get followed by many and without hesitation.

2) Interesting People - If you consistantly tweet about interesting topics or provide a service that people want, you should get plenty of followers without much of a concentrated effort.

3) People That Follow Back - There are 10's of thousands of people on Twitter that will followback, all you have to do is connect with them. This is the category that most Twitter users fall under, so that is what I'm going to talk most about.

The very first thing you need to do when opening a Twitter account is to go and read the Twitter Rules. Knowing the rules will prevent you from doing something that may get your account suspended.

Create Your Bio: You can write a good bio by simply letting people know who you are and what you're interested in.

Choose a Good Avatar: For personal accounts I suggest using a good photo of yourself. Face pics (head shots) are more effective than full length body shots. For business accounts, creating a good company logo is fine. You can do this online yourself through one of the many websites that provide this free service, or you can pay someone to have it done professionally.

Design Your Twitter Page: Simply personalize your background and right panel, and choose your text and link colors. You'll find it under the Profile link. I see so many people choosing the wrong combination of colors that it boggles the mind! White text/links or light colored text/links on a white background simply will not work! Needless to say, you can't read a damn word of it! Yeah, it's true. I've seen it with my own eyes. People really do this.

Follow Some People: The best way to find people to follow is to search for tweets with keywords related to what your interested in. As I said before, you need to find the people that are more likely to follow you back. I've found that you can safely follow as many as 100-200 people per day, without fear of violating Twitter Rules and risking account suspension. As your followers increase, so does the amount of people that you are allowed follow.

Determining Who Will Follow You Back Before following someone on Twitter, you need to pay strict attention to their Following to Followers ratio. If someone is for instance, following 1000 and only has 400 followers this is a prime target for you. Go ahead and follow them, more than likely they will follow you back. On the other hand, if someone follows only 100 people and has 3000 followers, chances are they will not follow you back. Just choose who you follow wisely. Also, it's important to let someone know that you just followed them too. After following someone send a NF(now following)@username tweet like this: "NF @username". This will show up in their Mentions list and more than likely they will follow back sooner. If after you have followed someone and you find that they haven't followed you back, simply remind them, or ask "can you follow me back?" Whatever you do, don't unfollow tons of people because they didn't follow you too. It's against Twitter Rules to do that. That's why it's so important to do a little research before following anyone you expect to follow you in return.

Other Things to Look for Before Following Someone Does there bio say I followback or do they claim to be 100% #TeamFollowBack or #Team4FollowBack? Once again, take a look at their following to followers ratio to determine if this is truly the case. A true Team4FollowBack user will have an almost even ratio. More times than not, they will be following more people than are following them.

As your Twitter presence increases and the shoe is on the other foot. People will begin following you first. If you don't want to have to search though all of your followers, which could be 1000's, to find who has followed you, so that you can follow back in return, you might consider using an auto follow back tool like this one Click Here. This tool automatically follows back any user that follows you. I've lost a bunch of followers in the past because I had no idea that I was not following some people back.

Avoid following inactive accounts! Look to see when they posted their last tweet. Personally, if someone hasn't tweeted in more than a week. I don't follow them.

Visibility:

This is probably the single most important ingredient to gaining followers.

Tweet, and tweet often. Someone once said to me, if you don't have anything interesting to say, "make something up!"

Search the web to find interesting topics. You can find many things to tweet from the internet.

Ask people to retweet you. Having your tweets retweeted greatly increases the chances of others seeing them, which in turn increases your chances of picking up more followers. At the end of your tweets just post "Plz Retweet" or "RT".

It's extremely important to use hashtags(#) in your tweets! The more you use them, the more your tweets will be seen. Just don't spam topics with unrelated tweets.