Wow! I'm surprised no one has responded to this.
Instagram has become a game changer for many businesses, similar to facebook changed digital marketing for ever back in 2004-2005.
First let me start by saying that in order to play the Instagram game, you must not play it like you do on Facebook.
Instagram marketing is all about getting to the trending feature of the main search page of the app. But although relatively speaking it should be easy since all you need is a Like, the psychology isn't like in Facebook where Likes are abound and freely given while shares are the kept only for valuable precious content - Instagram Likes are like Facebook Shares. both kind of hard to get for most businesses.

My name is Humberto Valle, I run a small digital marketing agency (www.Unthink.me) where we bring big business tools and experts to small growing companies. At Unthink, we play the game for several clients of ours (from celebrities, products, and teen influencers) here are some rules we crafted and follow that increase the chances for higher engagement on any given post:

--> this is assuming that by "selling" you mean generating traffic to sell and not the actual technical aspect of an API or software<---
1. Always, or at least 99% of the time show a face, your face, and no more than 3-4 people per image.
2. If you are monetizing or want to influence, you must never post before looking for relevant hashtags to use. Make sure to have a "Notes" on your phone so you can copy/paste them with ease each time. Instagram won't allow more than 30 #'s from last time I checked.
3. Unless you've spent a lot of money driving awareness to your logo, never start off with a logo in a profile picture. Have a professional picture of you, group, etc with branding but not just the logo.
4.Boosting posts: If you are to boost any post, make sure that is one that tells a story. Something that your target audience can see and instantly know what it is that's going on. Boosting posts is something any one with many followers does or has done to start.
5. Search for current buyers/users and Repost their content on your own feed. *you can use these images to announce a giveaway of sorts for others*
6. Boost user posts. (hire an agency if you have to get the right audience crafted for you)
7. Look for influencers but don't get greedy with their followers. Truth is that most people are not oblivious as to the value of having hundreds of thousands or millions of followers and so getting them to give you a mention or product placement post shot out will be nearly impossible unless you offer thousands. Instead, go for non-commercial influencers who simply enjoy posting and have no more than 20k or so followers. Make sure they are specific to your niche. Consider boosting a repost from them to be cross beneficial.
8. Steal competitor's followers by following them first and then going into each "liker's" profile page and liking, commenting or DM them when possible.
9. Use tools like https://boo.st/ to help you monetize. Use platforms like https://web.stagram.com/ to help you find the most trending influencer, hashtags, and posts in any given niche.
10. Use the live and timeline videos as much as possible to stay on top of mind of your current followers, don't focus only on acquiring new and ignore the existing.

I hope this has helped you, there isn't a black and white list of things to do to be successful, instead assume originality, post about yourself, make others smile and you are sure to have high engagements and ROI.