If you are a girl that stencils in her brows be very cautious about the shade and how much you put in. Do not fill them in over your natural shape, you'll look like that dog with eyebrows.
Also don't shade them a unnatural color to your natural brows.
Here are some good and bad picture comparisons.
Miss Katy Perry has matured with looks very well. Here brow shape is less stressed looking and filled in perfectly, unlike before.