I used this method to grow two twitter accounts to 10K in just 3 months.
Step 1: Use tools like MassPlanner or any chrome extension which can follow your target audience. I used Twitter Mass Follow chrome extention to follow good accounts. (Remember to flush out non-followers, inactive, non-English followers, and spammy accounts).
Note: You have to stay within Twitter limits. Do not follow more than 1000 accounts per day. You can change settings of the chrome extension and make it follow only 1000 accounts per day. It's super easy.
Step 2: Have a list of active Twitter followers who like, retweet and reply to you often. Put them on a private or public Twitter list. Engage with them whenever possible.
If you really don't have time, just install "Like all, plus all, favorite all" chrome extension and it can like and retweet tweets for you as you instruct it.
Step 3: Promote your friends content. Maintain a 3:1 ratio. Out of every four tweets, three tweets should be about others or any educating tweet and one tweet should be self promotional. If you promote other people's content, they might want to reciprocate and promote yours.
This is the easiest way to grow your Twitter account. If you are consistent you can get over 50K followers in a year without doing anything manually. You just need to set those extensions and tools will work for you. As they say - Automation does not mean you don't have to do anything. It does requires a bit of human interaction too.
Do you have tips to grow your Twitter audience? Feel free to share with us in the comments below.
P.S. I'm in for the Giveaway.