Think about this really quick: when you go into a room, where does light typically come from. Most people really prefer the look of lamp lighting. But the truth is that most light that we see actually comes from above us in some way or another. Think about the sun, or street lamps, or the ceiling in an office. All of these lights are from above.
So one of the ways that you can make flash output or off-camera lighting look more natural is to place the light source above your subject in some way or another. It could be in front and above, to the side and above, etc. This is just how we naturally see light. So when you place a flash in a scene, you typically shouldn’t light a subject from below. Think about placing your light source kind of like adding light to a room or a scene overall. Think about and consider the shape of it too.
This isn’t just how you’ll make the light look more appealing and flattering, but how you’ll also make it just look and seem more natural–by placing the center of the source above a person you’re photographing.