This depends on the type of audience you're targeting, but I have three general pieces of advice.

1. Test Your Content. No one has a magic bullet that works 100 percent of the time, but if you do A/B testing with your content (this should happen on all marketing efforts, not just Facebook or Instagram), you'll succeed more often than not. Run the same copy with two different images. Take the same engaging video for two posts, but ask a question in one and give a call-to-action in the other. Look at your analytics to see which one is working better and put more resources behind that.
2. Utilize Instagram Stories. They're an easy way to engage with people outside of your followers, even if you don't put any money behind it. And if you DO put money in your stories, you can effectively link to a product or service right there in your story (you can do that without paying if you have at least 10,000 followers already). Pro tip: Write several relevant hashtags but hide them behind a gif or emoji. People will still be able to access your content via those hashtags, but your image won't be covered with text.
3. Keep your brand voice. So often I'll see a brand that's fun and jovial on their posts, but then their ads read as stiffly as a ventriloquist's dummy. This is your chance to get your work out in front of a wider audience, but don't lose what makes you unique.

Hope that helps – best of luck! Happy to answer any additional questions.