If it's a camera with built-in meter, I just use that, with perhaps some compensation if it's a dark or bright scene.
Un-metered, I use an incident reading in the same light as the subject. If I can't use incident metering, then I'll take a reflected reading (usually using a light meter app on my phone that allows me to zoom in on the scene to match the camera's field of view). Again, I might adjust settings depending on the scene, but mostly I don't.