The goal is to take a photo that best represents the artwork the Buyer will receive. To do that it's better to hang your artwork to a wall at the height where the middle of your work will be and parallelly to the angle your camera is pointing to. Choose a wall that is of neutral color! Avoid direct light, since that can create glare and affect the colors. Make sure that your photo is of sufficient quality (minimum of 1200px) and that the colors in the photo fit the colors of the artwork in real life!