Says David Maderich, freelance makeup artist:

"The first step to
achieve the perfect brow is to decide on a shape. I prefer a thicker
brow with a soft defined arch. Remember, the archs highpoint should be
at the outer corner of the eyeball and then taper off.

To begin
your brow, find yourself a creamy white-eye pencil. Using your pencil,
trace under the brow to achieve the shape and arch you want then pluck
every hair in the white-penciled area. Next, comb hairs downward and
trim any strays..."

To read the rest of his great tips, go to http://modernsalon.com/Blog.aspx?oid=1081260