Top follower accounts: influencooors / people that are friends with top follower accounts and get boosted by them constantly / genuinely great people that actually deserve the massive following.

High follower accounts: Very, very active with a fair degree of help from big account boosts.

Mid follower accounts: Active and engaging with many others, often more quality content than top and high follower counts but post less often and have few big accounts that boost them, if any at all.

Low follower accounts: new here and/or possibly relay ignorance.

Bottom follower accounts: new here or no engaging with other people and not understanding there's no algorithm / Malicious Bots

But as to your actual question, seems to me the magic formula is:

● post very often, even to the degree that most posts aren't really of high quality.

● get boosted by top accounts (the hardest to do if you're not buddies with them, but the most effective way to get followers)

● engage with a loooot of people

● hashtags could help but at this point only modestly

I came to this conclusion when I noticed my follower account would not rise for shit when I posted unfrequently, even though I put much work into every post I did make. My longform article for example didn't do much for followers but more frequent lower quality posts did. Unfortunate but it is what it is.