That´s kinda generic question. To answer it completely will demand days, even weeks or months. But generally speaking, you´ll need a sales funnel.
Most traffic sources do not really like those three niches you´ve mentioned. So you´ll probably need to take a soft approach.
But WTF that means?
It means you gotta have to build one or both of these two things:
1) A landing page with some kinda offer on it, like a valuable Lead Magnet, a webinar, a free demo, but you gotta be careful with your wording and aggressiveness.
2) A website with some content (i.e., educational, news, insights, etc.) on it and then some sort of lead capture.
So after capturing the lead, you´ll guide them through your funnel, nurturing them and warming them up until it´s time to present the offer.
This is one of many approaches.
Another one is to choose traffic sources where there’s good volume available in tandem with relaxed rules to run your affiliate campaigns. This includes push, native, pop-ups, etc.
This way, your funnel can be much smaller. Usually, just from the traffic source to the landing page, then the offer, might work, but it also depends on many unknowns. For example, the type of conversion flow: CPL (SOI, DOI, CC), CPA, etc.
This is just my 2 cents to spark the conversation because, as I said, we would be talking about it for days and still just scratching the surface on methods to promote those niches.