Look at other ads that are attractive, try to do the same.
Here is what I do.
(1)Outdoors, slightly overcast(no shadows but brite)The white cardboard trick, reflecting the light will make your pics a touch better than the others.
(2)Tripod with hands off timer.
(3)Neutral background(not black or white)
(4)Keep background clutter to minimum.
(5)Crop, adjust brightness, correct tint(saturation), sharpen, size for internet(about 440px wide)