No matter how good (or bad) your content is, you can't gain new followers by posting content alone. You must always find ways to reach people outside of your following. Here are the best ways to increase the odds of expanding your audience.
1. Like, Comment, & Follow
Many people don't realize you can get followers without actively posting content. Every time you like, comment, or follow someone you put your name out there for other users to see and encourage those creators to return the favor. For best results try reaching active users with similar tastes; search hashtags of topics you post about and engage with the most recent posts. In my opinion following other accounts is the most effective mode of engagement, as Instagram encourages users to follow back right within the notification tab.
2. Tag. Tag. Tag.
I'm talking hashtags, geotags, and tagging people. Every new tag is an opportunity to reach people looking at these subjects. Tagging people and places is pretty straight forward, however many people do not how to best use hashtags. As a rule of thumb hashtags should be simple, searchable words that describe your content. You can keep your captions clean by typing the hashtags in the comment section after your content is posted. If you have trouble coming up with hashtags I highly recommend the free app, Focalmark, which automatically generates hashtags specific to your content.
3. Post Frequently
This should really go without saying, but if your goal is to get more followers you should post more often. Presuming you are tagging properly, every new post is another opportunity to reach new people. Further, keeping an active page gives users a reason to follow you.
If you have any questions or comments, feel free to include them down below.