I made a post about it the other day, i will explain it a little more now. You will need 2 twitter accounts, your main and a older account (older the better because twitter is less strict on following limits) On the older account, go to famous twitters that are related to your main account. Mine is a personal account and i am a teenager, so i use famous youtubers and other famous people. Go to the profile and the followers tab. Follow a lot of them, some will follow back, some wont. On your main account, go to the followers tab and follow all of them. Since they followed you back on your spam account, they will follow you back almost 100% of the time (if its the same type of account, i use an old personal account ect.) You can and will have to unfollow the people who dont follow you back on your older account. I have gained over 500 followers with 2 hours work in 3 days.