Post pictures! That's what Instagram is for. If you are aiming to use any social media to promote your channel, just use the platform as it is intended to be used. Instagram is for photos, so if you're a fitness channel post picture of exercises you can do, or health tips. The stories can be used very well for this as well. You can either mention your channel/video in the description or leave a link, that's up to you.
But yeah, just use the platform where it's for! And put promotion second. Otherwise people will notice you're just there to advertise and they will lose interest.
