The frame of your eyes should be attractively shaped. Eyebrows should be plucked gently from underneath to form a clearly defined arch.
Here is a trick for finding out the correct length of your brows.
Hold a pencil in front of your nose and perpendicular to it, with its base being close to the outer nostril. The top end of the pencil will point to where the eyebrow line should begin.
Gradually shift to top end of the pencil until it crosses the extreme edge of the eye. The tip end of the pencil will indicate where the brow line should end.