How to Target Uncommon Niches?

So in my head I have an idea of an uncommon niche that I'd like to venture with. I wouldn't say its non-existent, but I haven't seen too many top-dogs in this niche, nor many pages regarding this in general. I'd also like to point out that I'm not trying to strike gold here. My main objective is to target this uncommon audience for future use.

For those that have experience in this, what would you say is the best way to properly engage and connect with an uncommon audience? In the past when I've tried to tap into slightly rarer niches, my engagement rates were suffering while growth wasn't benefiting.

Would appreciate any and all help.