Using some of the upgrades on the Starmaker page can help a ton with gaining and sustaining followers. Some upgrades allow you to run ad campaigns etc that sort of act as buffs for your pictures which help with gaining a lot more subs and followers.
You level up by taking pictures of Anna or doing certain events that gain exp and the exp bar is the pink line at the bottom of the screen. without spoilers you can reduce the follower loss at the end of weekends later with some story stuff.
For me I just kept grinding pictures each day at every possible location with the buffs until I hit 30k subs.