Apart from the page 0 guide (which doesntm't provide practical tips), I found two things incredibly helpful:
1. Rich meta description being picked up by google.
2. Google knowledge graph links.
Now, this isnt 100% concrete. I am not
@t0mmy and
@Leith who have large agenciesm i only know this from a couple client and a couple personal sites.
The trends I find are:
1. The better the google snip it for meta description the more likely to be '0'.
Google will not always register your desired mets description. But if your meta description is perfectly accurate and picked up by google, you have a better chance of getting featured snippet.
2. Knowledge Graph Links
The most common is wikipedia. I saw a strong trend of knowledge graph links that pointed to the desired page getting the rank zero spot.
3. Images
This is less technical but I have main two trends. One is you almost always have a featured image above snippet. And two, the image does not need to appear on page to appear above the snippet.
What does that mean for SEO? Having an amazing and unique image on your page helps appear above 'zero'.
But the image largely relies upon CTR.
Sorry this isn't more specific. I don't deal with this scenario often so my answer is less 'do it my way' than most of my responses, but since I doubt many others have niches with the featured snippet and managed to rank page one and get the snippet link, I thought my answer would help.