General rule of thumb for this is extremely simple.

Provide unique + high value + people will beat down your doors to give you money.

My typical way for doing this, for completely new niches, is to work Meetup. I you get in rooms with a few people, this provides a great venue for you to work out your sales pitch.

Refining your pitch... to where it's near pitch-less or such a soft sell, no one knows your selling.

First attend + network.

Next, speak for groups - Meetup, WordCamp (or similar for your niche), PubCon, Affiliate Summit.

Really any conference will do. All that's required is you bridge your topic to the conference.

Say you're running a Uber knock off, then go speak at WordCamps (several run every week somewhere in the world), about the technology of your product + likely you'll pickup 100 paid customers in only a few talks.

This technique can be applied to any niche.