Use the 'pencil rule' for general shape. Place a pencil alongside your nose. Your brows should begin at the edge of the pencil. Next, angle the pencil from your nose to the outer corner of your eye. Your brow should end roughly where it meets the pencil. Finally, look straight ahead in the mirror. The highest point of your arch should be approximately over the outer edge of your pupil.
To highlight the drama of your brows, apply a bit of light, shimmery eyeshadow under the highest point of the arch.
To keep your left and right brows as similar as possible, go back and forth as you add color; don't do one brow completely and then move on to the next.
Your brows don't need to be perfect mirror images of each other. Think of them more as sisters than identical twins.