If you've been following many people on Twitter, the chances are that some of them are not following you back. This becomes a problem when you reach Twitter's following limits. If you are following too many people who are not following you back, they will restrict you from adding any more followers.
This can be a problem! That is why you want to use sites such as Twitter Karma, which will show you who is following you and who is not. After a reasonable amount of time, you may want to un-follow people who are not following you back. This will open up your account to follow more people, who may follow you back.
Once you get enough followers, this will not be an issue for you. Your goal should be to become one of the most followed people in your niche. That'll really help you corner the Twitter market in that niche, and your number of subscribers will just grow over time.
You can also follow people manually by going into your Twitter account. However, it is much easier to make use of one of the tools that are out on the market. Thankfully, there are some IM'ers that have written an ebook covering everything there is to know about Twitter — including how to get many followers and how to quickly unfollow those who are not following you.
Since you don't have time to spend all day on Twitter, this is great news for you. Instead of manually unfollowing people, you really can do this on autopilot. Simply make sure you have invested in your Twitter education, and you'll easily be able to dominate your niche with this hot social networking platform.
It's not that you don't want to follow the people who are not following you — but you really do need that space. Do not feel bad for unfollowing people, as it will help you grow your business. Perhaps you will find them again, or they will find you, and you can follow them at that point.
For now, just keep your eye on the prize and realize that you need to grow your Twitter account into the thousands in order to see the level of traffic and sales that you desire. Twitter is so incredibly popular, and it will only become more popular over time. Take advantage of this by dominating Twitter in your niche.