Personally I prime mine the same as for beer, a half teaspoon per 12 oz or a full teaspoon for a bigger bottle, or 5/8 cup cane sugar per 5 gallons. Things to keep in mind:
Natural carbonation of cider is always somewhat of a crapshoot, especially if you use sorbate and/or sulfite.
In any case it always takes longer to carbonate than for beer, a month or two or even more.
You can use more priming sugar to help guarantee carbonation. However, gushers and bottle bombs remain a distinct possibility.
Even if you do everything right, often times it might turn out flat or just a slight hiss when you pop the top, even after months.
Forced carb is probably best.
On the other hand, flat cider tastes every bit as good as the carbonated stuff. Cider is much more like a wine than beer.
Don't expect your finished cider to taste like Angry Orchard or Woodchuck. The vast majority of homemade ciders do not taste anything like the mass commercial ciders. And they shouldn't. They make their ciders from concentrate. We don't have to, we're not trying to compete with beer drinkers.