One of the most used strategies to get a lot of free followers is to follow a lot of people. This is especially necessary for new instagram or twitter users. When you follow people, they become aware that you are on twitter or instagram and they can thus follow you back. It acts as a form of introduction for you into the social media platform you have just joined. It is almost a social media courtesy that once a person follows your account, you follow them back unless you are a celebrity or a social media bigwig.
It is thus important to look at the accounts you are following. Following celebrities will keep your timeline well entertained but they will most likely not follow back. You thus need to follow a lot of regular account so as to get your free followers. It is also good to look for accounts where the people have the same interests as you do. This will motivate them to follow back. You could also like some of their tweets or photos to increase the chances of a follow back.