I've used Instagram for about a dozen different brands over the years. I believe Instagram is absolutely a great tool to use to promote your videos & channel.
However, with social media content you have to treat it with a little finesse. You can't just post about your channel. In fact, depending on who you talk to, you only want to self promote 20-40% of your posts. The goal is engagement. Just like YouTube.
I've been able to grow my first 200 followers on most Instagram accounts within 7 days or less by doing a couple simple routine tasks.
1. Each post I make, I make it a habit to search hashtags I want to rank for and then I engage with different posts for at least 5 minutes. Meaning, I'll comment and like other content, but mostly I'll be in comments. It's important to stick with the 5 minutes for every post you make. It is for me at least or else I would forget to do it.
2. I always try to be topical when posting, also knowing my audience. You don't want to post content that's not relevant to your followers. Having a faithful 200 followers is better than having 2000 unengaged followers.
3. Post minimum once a day. I know it's a chore, trust me. But nowadays there's several social media scheduling apps that make batch posting easier. I've tried over a dozen. In fact, I wasn't pleased with all but 2-3 of them so I actually created my own. It'll be released next month.
4. Be genuine. Don't just post something like "Awesome." on another users thread. Find a unique point. I promise you'll have better success being the most unique comment than being one of the usual.
5. Repurpose your YouTube videos for more content. You can do this by making video clips of audio, converting to blogs, pictures highlighting specific texts, and more. Don't reinvent the wheel. Just make sure it's relevant and not repetitive.
6. On occasion feel free to DM another IG user a sincere compliment. Maybe say something like, I think you'd like this video I posted and share the link. You'll have better luck with personalized DMs sharing your link than just leaving it in your bio.
7. The big one. Never buy followers. Ever.
If I can help you out any more please let me know. I actually kinda miss building IG accounts.