To determine exactly where your brow should begin, hold a makeup brush or a pencil straight up and down against one nostril. Where the pencil lands by your brow is where it should begin. The brow should end a little past your eye (if it grows down too far it will drag your eyes down). If you have a natural arch, work with it. If you need to create one, look into your eyes. The arch of your eyebrow should fall directly above the outside of your iris. Using an eyebrow pencil, fill in the brow area that you want to preserve so you can pluck outside the edges.
Begin tweezing from underneath the brow, removing one hair at a time from the inside of the brow to the outside. If part of your brow is thin enough already, do not pluck that area. Pull hairs in the direction in which they grow. Next, using a small brush, brush your brows upward. If they are too long, trim them very conservatively, cutting only a tiny amount at a time.
Once your brows are well shaped, you can use a variety of products to enhance them or fill them in as needed. Check out brow fixers, tinted brow gels, brow powders and brow pencils.