Shooting a clip that actually swaps well
The footage that works is not the footage TikTok trends usually reward, so it is worth knowing the trade-off. Face swapping is frame-by-frame, so it is happiest when the subject is well lit, roughly facing the camera, and moving at a normal pace. Trending formats built on fast cuts, whip pans and rapid head movement are precisely the conditions that make a swap ghost.
If you are shooting specifically to swap, a talking-to-camera clip in even light is close to a guaranteed result. If you are swapping footage you already have, expect the calm sections to look great and the frenetic ones to be where artefacts show.