I have about 12k twitter followers. And people are saying that I can make money from it? How make money from such follower base?
Select a product from clickbank or any affiliate network suitable for your follower base. And then just promote it through your account. Its the simplest way.
Try using sponsored tweets those services pay you well if you have a followers base around 10-15 k.
You can write review about the products of any companies to do advertising for them.