"Be helpful on the internet"
People will follow you if you are saying things that actually help them. The most effective way is probably teaching something, although sharing your "behind the scenes" story can work as well.
0-10: Start with friends. If you're on twitter for example, following your friends will get you your first few follow-backs
10-50: decide what you're going to be "about". Don't tweet/post about everything - pick ONE or TWO major topics, and just post about those, with the goal of _helping_ people. Share your knowledge. Then, start replying with helpful posts to other big names.
50-100: same as 10-50. Make sure your bio is hyper focused on your one or two topics, and that you post consistently, and with posts that provide a ton of value. Answer people's questions in public.
How I did it:
exactly the same as above until about 500 followers on twitter. Then I had a _giant_ follow event with the twitter thread "Learn React in 10 Tweets": https://twitter.com/chrisachard/status/1175022111758442497
After that (and gaining several hundred followers in a day, then several thousand in a few more days), it became easier to get engagement on posts. Continue to be helpful to people, and people will continue to follow.
I wrote about the process here too: https://chrisachard.com/triple-your-twitter-following