Hey man, people have posted some great ideas so far and I just wanted to add a few things I've had work for me in the past.
One thing that is super important on IG more than any other platform is the use of hashtags. Try finding other popular accounts in your niche and see which hashtags they're using on their most popular posts. Once you get a few popular ones that are specific to your niche check out a site like "Webstagram" that keeps an updated list of the most popular hashtags on Instagram. You can add up to 30 hashtags per post so max it out!
Also, I wish I could find the exact percentage but I've read that when you follow someone, like a picture, and leave a comment they are (I believe it was) 27% more likely to follow you back. Go to the popular hashtags in your niche and take the time to scroll posts while following, liking, and leaving a quick comment. Then go to popular accounts in your niche and follow everyone who is liking their pictures as well.
I've found that on average around 10%-20% of people follow back, so if you follow 1,000 people I bet around 100-200 people will follow you. So then do this over and over again. Follow 1,000 people, get your followers, then use an app to unfollow everyone who didn't follow you back. I'm cheap and not a computer genius so I use the free app "Unfollowers For Instagram" on the Google Play store but I KNOW more technology advanced apps exist!
Anyway, I hope some of this helps, good luck!