Posting is not enough anymore. Just like you want to feel your followers need you and enjoy your posts, they want you to interact with them more often. People love famous personalities who treat their followers as friends or at least "guests" of their pages, not as a mass of random people.
To show how you appreciate their support, you may write captions or post stories directed to them. Also, it would be nice to ask their opinion about your outfits and content in general. Finally, we have Instagram polls to use in stories,
so you can ask them to choose between just two options — that's very simple but enjoyable.
After gathering a large group of keen fans, you can proceed to your first contest. Arrange a "giveaway" — we all love to receive free rewards. The other great example of the contest is profile advertising. Some of the budding models or photographers might enjoy if you'd tell a word about their pages.
Set simple rules for each contest: don't make your followers leave Instagram and visit some third-party sources, just ask them to like your 10 recent photos or take a screenshot of your "contest" post and publish it in their own feed. Both parties profit again: you receive a bunch of new followers, and your fans get a real chance to get something from you.