How to increase twitter followers?
This is a rather broad question.
There are various strategies and tools you can use to do this.
This article lists some good ones: http://www.stateofsearch.com/10-ways-to-increase-your-twitter-followers-10-essential-tools-to-do-it/
In addition, there are several threads in this forum that have roundly discussed this question. Please research them and join an open discussion or, after researching, start a thread with a specific question that is not already open.