In a nutshell, without engaging in spammy behavior on instagram (because most likely that will just lead to getting banned), do you best to grow a marketable following. You can do this by employing lots of methods that are talked about on this site, such as following other active accounts responsibly, posting content on schedule multiple times per day, and liking and commenting other people's related posts. You can use software to automate these jobs, but it's getting harder and harder to get by instagram's bot detection methods. Take a look at Jarvee if you're interested in automating, or maybe using some free python scripts (check out instapy-cli).
Once you have a sizeable following with good engagement, it's time to make some money. Hopefully you chose to focus on a specific niche. As an example, let's say all your posts revolve around car gadgets, and all the people who follow you are interested in that. From there you can start a shopify store, or your own ecommerce website with WooCommerce (Wordpress plugin, etc) and every fourth post you make or so on instagram, the thing you post about just happens to be for sale on your website with a link. You might even want to include a call to action by offering a coupon code, etc. Some people even get by with dropping shipping items they don't physically have, but that is getting harder and harder. Your best bet is to create a nice brand with a logo, and make everything look as unique as possible. You can source almost any product imaginable from Alibaba, or Aliexpress.
If selling products isn't your thing, you can also sell shoutouts that last a certain amount of time, or even sell the entire account to someone else who wants to monetize it. If you're good at growing followings, you could flip accounts too. So let's say you buy an account with 5k followers, and you grow it up to 100k. You just made bank.
Instead of growing an instagram account, you can also do the reverse, and just pay for posts/shoutouts on other people's instagram accounts, that feature your product with a link. If you have a good product that converts nicely, results can come in really fast. Just make sure the page you decide to advertise on matches the content and audience you want to reach.