Man, this is such a crucial thing to get right if you're gonna write in that territory. I see way too many fics that treat it like a simple plot device without any thought for the real-world implications.
For me, the absolute bedrock is explicit, ongoing consent negotiated out-of-scene before anything starts. That means characters discussing hard limits, safewords, aftercare needs—all of it. It can't just be implied or happen in the moment. Showing that negotiation on-page, even briefly, establishes the foundation. Then, respecting the safeword the instant it's used, no drama, no hesitation. The power of a good kidnapping scene comes from the terrifying illusion of non-consent, not the reality of it.
Another practice is avoiding blending this kink with actual trauma narratives. If a character has a past abduction or assault, throwing them into a consensual non-consent kidnapping scenario without extremely careful handling feels irresponsible. The fantasy relies on a clear separation from real harm.
Also, aftercare isn't optional. The scene shouldn't just end with the 'victim' being magically okay. Showing the drop, the reassurance, the processing—that's what makes it feel safe for the reader, too. It turns something that could be deeply unsettling into a story about trust and vulnerability.